feat: Implement blue theme with modern design

- Add Inter font from Google Fonts for modern typography
- Implement blue theme from shadcn.com (primary: blue)
- Add beautiful hero header with car icon
- Create Separator component for visual division
- Increase card padding (p-8) for better breathing room
- Larger card titles (text-2xl) for better hierarchy
- Improved spacing throughout (gap-8, py-12, etc.)
- Blue primary color (#3B82F6) with proper foregrounds
- Professional, modern look matching shadcn.com aesthetic

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

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

frontend/app/page.tsx

@@ -3,6 +3,8 @@
 import { useState } from 'react'
 import JourneyForm from './components/JourneyForm'
 import DataPreview from './components/DataPreview'
+import { Separator } from '@/components/ui/separator'
+import { Car } from 'lucide-react'
 
 export default function Home() {
   const [calculatedData, setCalculatedData] = useState(null)
@@ -10,18 +12,26 @@ export default function Home() {
   const [formData, setFormData] = useState(null)
 
   return (
-    <main className="min-h-screen p-8 md:p-12">
-      <div className="max-w-7xl mx-auto">
-        <div className="mb-8">
-          <h1 className="text-3xl font-bold tracking-tight mb-2">
-            Kniha Jízd
-          </h1>
-          <p className="text-muted-foreground">
-            Automatizovaný systém pro správu knihy jízd
-          </p>
+    <main className="min-h-screen">
+      <div className="max-w-7xl mx-auto px-6 py-12 md:px-12 md:py-16">
+        <div className="mb-12">
+          <div className="flex items-center gap-4 mb-4">
+            <div className="flex h-16 w-16 items-center justify-center rounded-2xl bg-primary text-primary-foreground">
+              <Car className="h-8 w-8" />
+            </div>
+            <div>
+              <h1 className="text-4xl font-bold tracking-tight">
+                Kniha Jízd
+              </h1>
+              <p className="text-lg text-muted-foreground mt-1">
+                Automatizovaný systém pro správu knihy jízd
+              </p>
+            </div>
+          </div>
+          <Separator className="mt-8" />
         </div>
 
-        <div className="grid grid-cols-1 xl:grid-cols-2 gap-6">
+        <div className="grid grid-cols-1 xl:grid-cols-2 gap-8">
           <JourneyForm
             onDataCalculated={setCalculatedData}
             setLoading={setLoading}