feat: implement navigation and dark/light theme system

Add complete navigation and theming infrastructure:

**Theme System:**
- ThemeProvider component with React Context
  - Supports light, dark, and system themes
  - Persists preference to localStorage
  - Auto-detects system theme preference
  - Listens for system theme changes
  - Smooth theme transitions

- ThemeToggle component
  - Sun/Moon icon toggle button
  - Accessible with ARIA labels
  - Shows current theme state
  - Keyboard accessible

**Navigation:**
- Navbar component with sticky header
  - Gradient logo with Palette icon
  - Desktop horizontal navigation
  - Mobile responsive menu
  - Active route highlighting
  - Backdrop blur effect
  - Links to all main sections:
    - Home
    - Playground
    - Palettes
    - Accessibility
    - Named Colors
    - Batch Operations

**Layout Updates:**
- Integrated Navbar into root layout
- Added ThemeProvider to Providers wrapper
- Proper HTML suppressHydrationWarning for theme
- Container-based responsive layout

**Features:**
- Theme persists across page reloads
- System theme preference detection
- Active navigation state
- Smooth hover transitions
- Mobile-first responsive design
- Accessible navigation with proper semantics

**Styling:**
- Gradient text logo (pink → purple → blue)
- Sticky top navbar with backdrop blur
- Border bottom for visual separation
- Consistent spacing and padding
- Mobile menu slides in smoothly

Build successful! Navigation and theming complete.

Next: Palette generation pages and additional features.

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

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

components/providers/Providers.tsx

@@ -3,6 +3,7 @@
 import { QueryClient, QueryClientProvider } from '@tanstack/react-query';
 import { Toaster } from 'sonner';
 import { useState } from 'react';
+import { ThemeProvider } from './ThemeProvider';
 
 export function Providers({ children }: { children: React.ReactNode }) {
   const [queryClient] = useState(
@@ -18,9 +19,11 @@ export function Providers({ children }: { children: React.ReactNode }) {
   );
 
   return (
-    <QueryClientProvider client={queryClient}>
-      {children}
-      <Toaster position="top-right" richColors />
-    </QueryClientProvider>
+    <ThemeProvider>
+      <QueryClientProvider client={queryClient}>
+        {children}
+        <Toaster position="top-right" richColors />
+      </QueryClientProvider>
+    </ThemeProvider>
   );
 }

components/providers/ThemeProvider.tsx

@@ -0,0 +1,78 @@
+'use client';
+
+import { createContext, useContext, useEffect, useState } from 'react';
+
+type Theme = 'light' | 'dark' | 'system';
+
+interface ThemeContextType {
+  theme: Theme;
+  setTheme: (theme: Theme) => void;
+  resolvedTheme: 'light' | 'dark';
+}
+
+const ThemeContext = createContext<ThemeContextType | undefined>(undefined);
+
+export function ThemeProvider({ children }: { children: React.ReactNode }) {
+  const [theme, setTheme] = useState<Theme>('system');
+  const [resolvedTheme, setResolvedTheme] = useState<'light' | 'dark'>('light');
+
+  useEffect(() => {
+    // Load theme from localStorage
+    const stored = localStorage.getItem('theme') as Theme | null;
+    if (stored) {
+      setTheme(stored);
+    }
+  }, []);
+
+  useEffect(() => {
+    const root = window.document.documentElement;
+
+    // Remove previous theme classes
+    root.classList.remove('light', 'dark');
+
+    if (theme === 'system') {
+      const systemTheme = window.matchMedia('(prefers-color-scheme: dark)').matches
+        ? 'dark'
+        : 'light';
+      root.classList.add(systemTheme);
+      setResolvedTheme(systemTheme);
+    } else {
+      root.classList.add(theme);
+      setResolvedTheme(theme);
+    }
+
+    // Save to localStorage
+    localStorage.setItem('theme', theme);
+  }, [theme]);
+
+  // Listen for system theme changes
+  useEffect(() => {
+    const mediaQuery = window.matchMedia('(prefers-color-scheme: dark)');
+
+    const handleChange = () => {
+      if (theme === 'system') {
+        const systemTheme = mediaQuery.matches ? 'dark' : 'light';
+        setResolvedTheme(systemTheme);
+        window.document.documentElement.classList.remove('light', 'dark');
+        window.document.documentElement.classList.add(systemTheme);
+      }
+    };
+
+    mediaQuery.addEventListener('change', handleChange);
+    return () => mediaQuery.removeEventListener('change', handleChange);
+  }, [theme]);
+
+  return (
+    <ThemeContext.Provider value={{ theme, setTheme, resolvedTheme }}>
+      {children}
+    </ThemeContext.Provider>
+  );
+}
+
+export function useTheme() {
+  const context = useContext(ThemeContext);
+  if (context === undefined) {
+    throw new Error('useTheme must be used within a ThemeProvider');
+  }
+  return context;
+}