feat(app): add sliding sidebar navigation for mobile

- Homepage now shows "New Agent" form, agent list moves to sidebar
- Hamburger menu replaces back arrow on all screens
- Mobile: full-screen sidebar overlay with swipe-to-close gesture
- Desktop: fixed 320px sidebar, toggle via hamburger
- Smooth bezier-eased animations (220ms)
- Sidebar closes on agent select (mobile only)

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

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

packages/app/src/components/home-footer.tsx

@@ -163,7 +163,7 @@ export function HomeFooter() {
             <Pressable
               onPress={() => {
                 console.log("[HomeFooter] New Agent button pressed");
-                router.push("/agent/new");
+                router.push("/");
               }}
               style={({ pressed }) => [
                 styles.footerButton,