chore: bump version to 2.0.8, replace static README badge with dynamic GitHub Release badge

- Layout.tsx: v2.0.7 → v2.0.8
- cmd/server/main.go: 2.0.7 → 2.0.8
- README.md: static version badge → shields.io/github/v/release (auto-updates)

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

web/src/components/Layout.tsx

@@ -69,7 +69,7 @@ export default function Layout() {
         </nav>
 
         <div className="px-5 py-3 border-t border-white/10 flex items-center justify-between">
-          <span className="text-[10px] text-brand-300/60 font-mono">v2.0.7</span>
+          <span className="text-[10px] text-brand-300/60 font-mono">v2.0.8</span>
           {authRequired && (
             <button
               onClick={logout}