Add bundle analyzer configuration

Configure @next/bundle-analyzer for production bundle analysis:

**Changes:**
- Install @next/bundle-analyzer package
- Update next.config.mjs to wrap config with bundle analyzer
- Add npm script `build:analyze` to run build with ANALYZE=true
- Bundle analyzer only enabled when ANALYZE=true environment variable is set

**Usage:**
```bash
# Run build with bundle analysis
npm run build:analyze

# Opens interactive bundle visualization in browser
# Shows chunk sizes, module dependencies, and optimization opportunities
```

**Note:** Kept Mastodon feed as Client Component (not Server Component)
because formatRelativeTime() uses `new Date()` which requires dynamic
rendering. Converting to Server Component would prevent static generation.

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

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

components/layout-shell.tsx

@@ -1,6 +1,5 @@
 import { SiteHeader } from './site-header';
 import { SiteFooter } from './site-footer';
-
 import { BackToTop } from './back-to-top';
 
 export function LayoutShell({ children }: { children: React.ReactNode }) {