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>

apps/editor/app/globals.css

@@ -119,6 +119,21 @@
   body {
     @apply bg-background text-foreground;
   }
+  button,
+  [role="button"],
+  a {
+    cursor: pointer;
+  }
+}
+
+/* Apple-style smooth corners (squircle) — progressive enhancement */
+.rounded-smooth {
+  border-radius: var(--radius-lg);
+  corner-shape: squircle;
+}
+.rounded-smooth-xl {
+  border-radius: var(--radius-xl);
+  corner-shape: squircle;
 }
 
 .no-scrollbar::-webkit-scrollbar {