feat: add Google OAuth, user profiles, community hub improvements

- Add Google OAuth sign-in alongside magic link authentication
- Username onboarding: require username selection after first sign-in
- Public profile pages at /u/[username] with social links (GitHub, X)
- Settings page for managing username and social links
- Viewer header: unified floating card with project name, @username, breadcrumb
- Guest CTA on viewer page prompting sign-in
- Show owner avatar + username on community project cards
- Redesigned project cards (larger preview, avatar + stats row below)
- Consistent navbar across hub and profile pages with GitHub link
- Footer with links to GitHub repo and npm packages
- Borderless design with natural shadows throughout
- Apple corner smoothing (squircle) progressive enhancement
- cursor:pointer globally on buttons and links
- DB migrations: username, github_url, x_url columns on auth_users
- Root-level db:generate/migrate/push/studio scripts

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

package.json

@@ -12,6 +12,10 @@
     "check:fix": "biome check --write",
     "check-types": "turbo run check-types",
     "kill": "lsof -ti:3002 | xargs kill -9 2>/dev/null || echo 'No processes found on port 3002'",
+    "db:generate": "bun run --cwd packages/db db:generate",
+    "db:migrate": "bun run --cwd packages/db db:migrate",
+    "db:push": "bun run --cwd packages/db db:push",
+    "db:studio": "bun run --cwd packages/db db:studio",
     "db:start": "supabase start",
     "db:stop": "supabase stop",
     "db:reset": "supabase db reset",