Final working solution: shadcn date picker with timezone fix

- Implemented shadcn/ui date picker with Czech localization
- Added month/year dropdown navigation for easy date selection
- Fixed critical timezone bug causing "No valid days found" error
  - Changed from toISOString() to local date formatting
  - Dates now correctly sent as 2025-01-01 instead of 2024-12-31
- Calendar auto-closes after date selection
- All features tested and working:
  - Journey calculation with correct date ranges
  - "Vyplnit na web" button visible and functional
  - Excel export working
  - Backend successfully processes January 2025 data

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

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

frontend/tailwind.config.js

@@ -1,45 +1,55 @@
 /** @type {import('tailwindcss').Config} */
 module.exports = {
+  darkMode: ["class"],
   content: [
-    './pages/**/*.{js,ts,jsx,tsx,mdx}',
-    './components/**/*.{js,ts,jsx,tsx,mdx}',
-    './app/**/*.{js,ts,jsx,tsx,mdx}',
+    './pages/**/*.{ts,tsx}',
+    './components/**/*.{ts,tsx}',
+    './app/**/*.{ts,tsx}',
+    './src/**/*.{ts,tsx}',
   ],
+  prefix: "",
   theme: {
+    container: {
+      center: true,
+      padding: "2rem",
+      screens: {
+        "2xl": "1400px",
+      },
+    },
     extend: {
       colors: {
-        border: "hsl(var(--color-border))",
-        input: "hsl(var(--color-input))",
-        ring: "hsl(var(--color-ring))",
-        background: "hsl(var(--color-background))",
-        foreground: "hsl(var(--color-foreground))",
+        border: "hsl(var(--border))",
+        input: "hsl(var(--input))",
+        ring: "hsl(var(--ring))",
+        background: "hsl(var(--background))",
+        foreground: "hsl(var(--foreground))",
         primary: {
-          DEFAULT: "hsl(var(--color-primary))",
-          foreground: "hsl(var(--color-primary-foreground))",
+          DEFAULT: "hsl(var(--primary))",
+          foreground: "hsl(var(--primary-foreground))",
         },
         secondary: {
-          DEFAULT: "hsl(var(--color-secondary))",
-          foreground: "hsl(var(--color-secondary-foreground))",
+          DEFAULT: "hsl(var(--secondary))",
+          foreground: "hsl(var(--secondary-foreground))",
         },
         destructive: {
-          DEFAULT: "hsl(var(--color-destructive))",
-          foreground: "hsl(var(--color-destructive-foreground))",
+          DEFAULT: "hsl(var(--destructive))",
+          foreground: "hsl(var(--destructive-foreground))",
         },
         muted: {
-          DEFAULT: "hsl(var(--color-muted))",
-          foreground: "hsl(var(--color-muted-foreground))",
+          DEFAULT: "hsl(var(--muted))",
+          foreground: "hsl(var(--muted-foreground))",
         },
         accent: {
-          DEFAULT: "hsl(var(--color-accent))",
-          foreground: "hsl(var(--color-accent-foreground))",
+          DEFAULT: "hsl(var(--accent))",
+          foreground: "hsl(var(--accent-foreground))",
         },
         popover: {
-          DEFAULT: "hsl(var(--color-popover))",
-          foreground: "hsl(var(--color-popover-foreground))",
+          DEFAULT: "hsl(var(--popover))",
+          foreground: "hsl(var(--popover-foreground))",
         },
         card: {
-          DEFAULT: "hsl(var(--color-card))",
-          foreground: "hsl(var(--color-card-foreground))",
+          DEFAULT: "hsl(var(--card))",
+          foreground: "hsl(var(--card-foreground))",
         },
       },
       borderRadius: {
@@ -47,7 +57,21 @@ module.exports = {
         md: "calc(var(--radius) - 2px)",
         sm: "calc(var(--radius) - 4px)",
       },
+      keyframes: {
+        "accordion-down": {
+          from: { height: "0" },
+          to: { height: "var(--radix-accordion-content-height)" },
+        },
+        "accordion-up": {
+          from: { height: "var(--radix-accordion-content-height)" },
+          to: { height: "0" },
+        },
+      },
+      animation: {
+        "accordion-down": "accordion-down 0.2s ease-out",
+        "accordion-up": "accordion-up 0.2s ease-out",
+      },
     },
   },
-  plugins: [],
+  plugins: [require("tailwindcss-animate")],
 }