Add full-text search with Chinese tokenization using Pagefind

Integrated Pagefind for static site search with built-in Chinese word segmentation support.

Changes:
1. **Installed Pagefind** (v1.4.0) as dev dependency
2. **Updated build script** to run Pagefind indexing after Next.js build
   - Indexes all 69 pages with 5,711 words
   - Automatic Chinese (zh-tw) language detection
3. **Created search modal component** (components/search-modal.tsx)
   - Dynamic Pagefind UI loading (lazy-loaded on demand)
   - Keyboard shortcuts (Cmd+K / Ctrl+K)
   - Chinese translations for UI elements
   - Dark mode compatible styling
4. **Added search button to header** (components/site-header.tsx)
   - Integrated SearchButton with keyboard shortcut display
   - Modal state management
5. **Custom Pagefind styles** (styles/globals.css)
   - Tailwind-based styling to match site design
   - Dark mode support
   - Highlight styling for search results

Features:
- ✅ Full-text search across all blog posts and pages
- ✅ Built-in Chinese word segmentation (Unicode-based)
- ✅ Mixed Chinese/English query support
- ✅ Zero bundle impact (20KB lazy-loaded on search activation)
- ✅ Keyboard shortcuts (⌘K / Ctrl+K)
- ✅ Search result highlighting with excerpts
- ✅ Dark mode compatible

Technical Details:
- Pagefind runs post-build to index .next directory
- Search index stored in .next/pagefind/
- Chinese segmentation works automatically via Unicode boundaries
- No third-party services or API keys required

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

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

components/site-header.tsx

@@ -1,10 +1,15 @@
+'use client';
+
 import Link from 'next/link';
+import { useState } from 'react';
 import { ThemeToggle } from './theme-toggle';
 import { NavMenu, NavLinkItem, IconKey } from './nav-menu';
+import { SearchButton, SearchModal } from './search-modal';
 import { siteConfig } from '@/lib/config';
 import { allPages } from 'contentlayer2/generated';
 
 export function SiteHeader() {
+  const [isSearchOpen, setIsSearchOpen] = useState(false);
   const pages = allPages
     .slice()
     .sort((a, b) => (a.title || '').localeCompare(b.title || ''));
@@ -32,8 +37,13 @@ export function SiteHeader() {
         </Link>
         <div className="flex items-center gap-3">
           <NavMenu items={navItems} />
+          <SearchButton onClick={() => setIsSearchOpen(true)} />
           <ThemeToggle />
         </div>
+        <SearchModal
+          isOpen={isSearchOpen}
+          onClose={() => setIsSearchOpen(false)}
+        />
       </div>
     </header>
   );