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/lib/auth.ts

@@ -12,6 +12,8 @@ export const auth = createAuth({
   appName: 'Pascal Editor',
   baseURL: BASE_URL,
   secret: process.env.BETTER_AUTH_SECRET!,
+  googleClientId: process.env.GOOGLE_CLIENT_ID,
+  googleClientSecret: process.env.GOOGLE_CLIENT_SECRET,
   sendMagicLink: async ({ email, url }) => {
     if (!resend) {
       console.log(`[DEV] Magic link for ${email}: ${url}`)