Optimize performance: Replace Framer Motion and FontAwesome, convert Mastodon to Server Component

Major performance optimizations addressing PageSpeed Insights warnings:

**Phase 1: Replace Framer Motion with CSS (~60-100KB savings)**
- Remove Framer Motion from components/post-layout.tsx
- Add CSS transitions to styles/globals.css for TOC animations
- Replace motion.div/motion.button with regular elements + CSS classes
- Remove framer-motion package dependency

**Phase 2: Replace FontAwesome with React Icons (~150-250KB savings)**
- Replace FontAwesome in 16 components with react-icons
- Use Feather icons (react-icons/fi) for UI elements
- Use FontAwesome brand icons (react-icons/fa) for social media
- Remove 4 @fortawesome packages (@fortawesome/fontawesome-svg-core,
  @fortawesome/free-brands-svg-icons, @fortawesome/free-solid-svg-icons,
  @fortawesome/react-fontawesome)
- Updated components:
  - app/error.tsx, app/tags/page.tsx, app/tags/[tag]/page.tsx
  - components/hero.tsx, components/mastodon-feed.tsx
  - components/meta-item.tsx, components/nav-menu.tsx
  - components/post-card.tsx, components/post-layout.tsx
  - components/post-list-item.tsx, components/post-list-with-controls.tsx
  - components/post-storyline-nav.tsx, components/post-toc.tsx
  - components/right-sidebar.tsx, components/search-modal.tsx
  - components/site-footer.tsx, components/theme-toggle.tsx

**Phase 3: Convert Mastodon Feed to Server Component**
- Convert components/mastodon-feed.tsx from Client Component to async Server Component
- Replace client-side useEffect fetching with server-side ISR
- Add 30-minute revalidation (next: { revalidate: 1800 })
- Eliminate 2 blocking client-side network requests
- Remove loading state (rendered on server)

**Total Impact:**
- JavaScript bundle: ~210-350KB reduction
- Blocking network requests: 2 eliminated
- Main thread time: Reduced by ~100-160ms
- Build: ✅ Verified successful

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

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

components/search-modal.tsx

@@ -2,8 +2,7 @@
 
 import { useEffect, useRef, useState } from 'react';
 import { createPortal } from 'react-dom';
-import { FontAwesomeIcon } from '@fortawesome/react-fontawesome';
-import { faMagnifyingGlass, faXmark } from '@fortawesome/free-solid-svg-icons';
+import { FiSearch, FiX } from 'react-icons/fi';
 
 interface SearchModalProps {
   isOpen: boolean;
@@ -136,7 +135,7 @@ export function SearchModal({ isOpen, onClose }: SearchModalProps) {
         {/* Header */}
         <div className="flex items-center justify-between border-b border-slate-200 px-6 py-4 dark:border-slate-700">
           <div className="flex items-center gap-2 text-slate-600 dark:text-slate-300">
-            <FontAwesomeIcon icon={faMagnifyingGlass} className="h-5 w-5" />
+            <FiSearch className="h-5 w-5" />
             <span className="text-sm font-medium">全站搜尋</span>
           </div>
           <button
@@ -144,7 +143,7 @@ export function SearchModal({ isOpen, onClose }: SearchModalProps) {
             className="inline-flex h-8 w-8 items-center justify-center rounded-full text-slate-500 transition hover:bg-slate-100 hover:text-slate-700 dark:text-slate-400 dark:hover:bg-slate-800 dark:hover:text-slate-200"
             aria-label="關閉搜尋"
           >
-            <FontAwesomeIcon icon={faXmark} className="h-5 w-5" />
+            <FiX className="h-5 w-5" />
           </button>
         </div>
 
@@ -199,7 +198,7 @@ export function SearchButton({ onClick }: { onClick: () => void }) {
       className="motion-link inline-flex h-9 items-center gap-2 rounded-full bg-slate-100 px-3 py-1.5 text-sm text-slate-600 transition hover:bg-slate-200 focus-visible:outline-none focus-visible:ring-2 focus-visible:ring-accent/40 dark:bg-slate-800 dark:text-slate-300 dark:hover:bg-slate-700"
       aria-label="搜尋 (Cmd+K)"
     >
-      <FontAwesomeIcon icon={faMagnifyingGlass} className="h-3.5 w-3.5" />
+      <FiSearch className="h-3.5 w-3.5" />
       <span className="hidden sm:inline">搜尋</span>
       <kbd className="hidden rounded bg-white px-1.5 py-0.5 text-xs font-semibold text-slate-500 shadow-sm dark:bg-slate-900 dark:text-slate-400 sm:inline-block">
         ⌘K