feat: Integrate shadcn/ui design system

- Install shadcn/ui dependencies (CVA, clsx, tailwind-merge, lucide-react)
- Install Radix UI primitives (slot, label)
- Create utility helper (lib/utils.ts with cn function)
- Update Tailwind config for shadcn/ui theme support
- Add CSS variables for theming in globals.css (Tailwind v4 syntax)
- Add shadcn/ui components: Button, Card, Input, Label
- Update JourneyForm with shadcn/ui components and icons
- Update DataPreview with shadcn/ui components and icons
- Improve UI consistency and accessibility

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

frontend/app/components/JourneyForm.tsx

@@ -2,6 +2,11 @@
 
 import { useState } from 'react'
 import API_URL from '@/lib/api'
+import { Button } from '@/components/ui/button'
+import { Input } from '@/components/ui/input'
+import { Label } from '@/components/ui/label'
+import { Card, CardContent, CardHeader, CardTitle } from '@/components/ui/card'
+import { Calculator, Download } from 'lucide-react'
 
 interface JourneyFormProps {
   onDataCalculated: (data: any) => void
@@ -99,130 +104,114 @@ export default function JourneyForm({ onDataCalculated, setLoading, onFormDataCh
   }
 
   return (
-    <div className="bg-white/98 backdrop-blur-lg rounded-3xl shadow-2xl overflow-hidden border border-white/30">
-      <div className="bg-gradient-to-r from-blue-50 to-blue-100 px-8 py-6 border-b border-blue-200">
-        <div className="flex items-center gap-4">
+    <Card className="bg-white/98 backdrop-blur-lg border-white/30">
+      <CardHeader className="bg-gradient-to-r from-blue-50 to-blue-100 border-b border-blue-200">
+        <CardTitle className="text-3xl font-bold text-gray-800 flex items-center gap-4">
           <div className="w-12 h-12 bg-gradient-to-br from-blue-500 to-blue-600 rounded-xl flex items-center justify-center shadow-lg">
             <svg className="w-7 h-7 text-white" fill="none" stroke="currentColor" viewBox="0 0 24 24">
               <path strokeLinecap="round" strokeLinejoin="round" strokeWidth={2} d="M11 5H6a2 2 0 00-2 2v11a2 2 0 002 2h11a2 2 0 002-2v-5m-1.414-9.414a2 2 0 112.828 2.828L11.828 15H9v-2.828l8.586-8.586z" />
             </svg>
           </div>
-          <h2 className="text-3xl font-bold text-gray-800">Vstupní údaje</h2>
-        </div>
-      </div>
-      <div className="p-8">
+          <span>Vstupní údaje</span>
+        </CardTitle>
+      </CardHeader>
+      <CardContent className="p-8">
 
       <form onSubmit={handleSubmit} className="space-y-5">
-        <div>
-          <label className="block text-sm font-medium text-gray-700 mb-1">
-            Uživatelské jméno
-          </label>
-          <input
+        <div className="space-y-2">
+          <Label htmlFor="username">Uživatelské jméno</Label>
+          <Input
+            id="username"
             type="text"
             required
             value={formData.username}
             onChange={(e) => setFormData({ ...formData, username: e.target.value })}
-            className="w-full px-4 py-3 bg-gray-50 border border-gray-200 rounded-lg focus:outline-none focus:ring-2 focus:ring-blue-500 focus:border-transparent transition-all"
             placeholder="Zadejte uživatelské jméno"
           />
         </div>
 
-        <div>
-          <label className="block text-sm font-medium text-gray-700 mb-1">
-            Heslo
-          </label>
-          <input
+        <div className="space-y-2">
+          <Label htmlFor="password">Heslo</Label>
+          <Input
+            id="password"
             type="password"
             required
             value={formData.password}
             onChange={(e) => setFormData({ ...formData, password: e.target.value })}
-            className="w-full px-4 py-3 bg-gray-50 border border-gray-200 rounded-lg focus:outline-none focus:ring-2 focus:ring-blue-500 focus:border-transparent transition-all"
             placeholder="Zadejte heslo"
           />
         </div>
 
         <div className="grid grid-cols-2 gap-4">
-          <div>
-            <label className="block text-sm font-medium text-gray-700 mb-1">
-              Datum od
-            </label>
-            <input
+          <div className="space-y-2">
+            <Label htmlFor="startDate">Datum od</Label>
+            <Input
+              id="startDate"
               type="date"
               required
               value={formData.startDate}
               onChange={(e) => setFormData({ ...formData, startDate: e.target.value })}
-              className="w-full px-4 py-3 bg-gray-50 border border-gray-200 rounded-lg focus:outline-none focus:ring-2 focus:ring-blue-500 focus:border-transparent transition-all"
             />
           </div>
 
-          <div>
-            <label className="block text-sm font-medium text-gray-700 mb-1">
-              Datum do
-            </label>
-            <input
+          <div className="space-y-2">
+            <Label htmlFor="endDate">Datum do</Label>
+            <Input
+              id="endDate"
               type="date"
               required
               value={formData.endDate}
               onChange={(e) => setFormData({ ...formData, endDate: e.target.value })}
-              className="w-full px-4 py-3 bg-gray-50 border border-gray-200 rounded-lg focus:outline-none focus:ring-2 focus:ring-blue-500 focus:border-transparent transition-all"
             />
           </div>
         </div>
 
         <div className="grid grid-cols-2 gap-4">
-          <div>
-            <label className="block text-sm font-medium text-gray-700 mb-1">
-              Počáteční stav [km]
-            </label>
-            <input
+          <div className="space-y-2">
+            <Label htmlFor="startKm">Počáteční stav [km]</Label>
+            <Input
+              id="startKm"
               type="number"
               required
               value={formData.startKm}
               onChange={(e) => setFormData({ ...formData, startKm: e.target.value })}
-              className="w-full px-4 py-3 bg-gray-50 border border-gray-200 rounded-lg focus:outline-none focus:ring-2 focus:ring-blue-500 focus:border-transparent transition-all"
             />
           </div>
 
-          <div>
-            <label className="block text-sm font-medium text-gray-700 mb-1">
-              Koncový stav [km]
-            </label>
-            <input
+          <div className="space-y-2">
+            <Label htmlFor="endKm">Koncový stav [km]</Label>
+            <Input
+              id="endKm"
               type="number"
               required
               value={formData.endKm}
               onChange={(e) => setFormData({ ...formData, endKm: e.target.value })}
-              className="w-full px-4 py-3 bg-gray-50 border border-gray-200 rounded-lg focus:outline-none focus:ring-2 focus:ring-blue-500 focus:border-transparent transition-all"
             />
           </div>
         </div>
 
-        <div>
-          <label className="block text-sm font-medium text-gray-700 mb-1">
-            SPZ vozidla
-          </label>
-          <input
+        <div className="space-y-2">
+          <Label htmlFor="vehicleRegistration">SPZ vozidla</Label>
+          <Input
+            id="vehicleRegistration"
             type="text"
             value={formData.vehicleRegistration}
             onChange={(e) => setFormData({ ...formData, vehicleRegistration: e.target.value })}
-            className="w-full px-4 py-3 bg-gray-50 border border-gray-200 rounded-lg focus:outline-none focus:ring-2 focus:ring-blue-500 focus:border-transparent transition-all"
           />
         </div>
 
-        <div>
-          <label className="block text-sm font-medium text-gray-700 mb-1">
-            Variance (0-1)
-          </label>
-          <input
+        <div className="space-y-2">
+          <Label htmlFor="variance">Variance (0-1)</Label>
+          <Input
+            id="variance"
             type="number"
             step="0.01"
             min="0"
             max="1"
             value={formData.variance}
             onChange={(e) => setFormData({ ...formData, variance: e.target.value })}
-            className="w-full px-4 py-3 bg-gray-50 border border-gray-200 rounded-lg focus:outline-none focus:ring-2 focus:ring-blue-500 focus:border-transparent transition-all"
           />
-          <p className="text-xs text-gray-500 mt-1">
+          <p className="text-xs text-muted-foreground">
             Náhodná variace rozdělení kilometrů (doporučeno 0.1 = 10%)
           </p>
         </div>
@@ -237,33 +226,27 @@ export default function JourneyForm({ onDataCalculated, setLoading, onFormDataCh
         )}
 
         <div className="flex flex-col sm:flex-row gap-4 pt-6">
-          <button
+          <Button
             type="submit"
-            className="flex-1 bg-gradient-to-r from-blue-600 to-blue-700 hover:from-blue-700 hover:to-blue-800 text-white font-bold py-4 px-6 rounded-xl shadow-lg hover:shadow-2xl transform hover:-translate-y-1 transition-all duration-200"
+            size="lg"
+            className="flex-1 bg-gradient-to-r from-blue-600 to-blue-700 hover:from-blue-700 hover:to-blue-800 text-lg h-12"
           >
-            <span className="flex items-center justify-center gap-3">
-              <svg className="w-6 h-6" fill="none" stroke="currentColor" viewBox="0 0 24 24">
-                <path strokeLinecap="round" strokeLinejoin="round" strokeWidth={2} d="M9 7h6m0 10v-3m-3 3h.01M9 17h.01M9 14h.01M12 14h.01M15 11h.01M12 11h.01M9 11h.01M7 21h10a2 2 0 002-2V5a2 2 0 00-2-2H7a2 2 0 00-2 2v14a2 2 0 002 2z" />
-              </svg>
-              <span className="text-lg">Vypočítat</span>
-            </span>
-          </button>
+            <Calculator className="mr-2 h-5 w-5" />
+            Vypočítat
+          </Button>
 
-          <button
+          <Button
             type="button"
             onClick={handleExport}
-            className="flex-1 bg-gradient-to-r from-green-600 to-green-700 hover:from-green-700 hover:to-green-800 text-white font-bold py-4 px-6 rounded-xl shadow-lg hover:shadow-2xl transform hover:-translate-y-1 transition-all duration-200"
+            size="lg"
+            className="flex-1 bg-gradient-to-r from-green-600 to-green-700 hover:from-green-700 hover:to-green-800 text-lg h-12"
           >
-            <span className="flex items-center justify-center gap-3">
-              <svg className="w-6 h-6" fill="none" stroke="currentColor" viewBox="0 0 24 24">
-                <path strokeLinecap="round" strokeLinejoin="round" strokeWidth={2} d="M12 10v6m0 0l-3-3m3 3l3-3m2 8H7a2 2 0 01-2-2V5a2 2 0 012-2h5.586a1 1 0 01.707.293l5.414 5.414a1 1 0 01.293.707V19a2 2 0 01-2 2z" />
-              </svg>
-              <span className="text-lg">Export Excel</span>
-            </span>
-          </button>
+            <Download className="mr-2 h-5 w-5" />
+            Export Excel
+          </Button>
         </div>
       </form>
-      </div>
-    </div>
+      </CardContent>
+    </Card>
   )
 }