feat: add user profile endpoints + language seed for LanguParent app

- users_public gets user_id FK (1:1 link to auth user)
- Seed languages: en, sv alongside existing de
- POST /auth/register + /auth/login now include needsProfile flag
- New JWT-authed endpoints (end-user allowed):
    GET  /auth/languages   public language list
    GET  /auth/check-username
    GET  /auth/me          full profile join
    POST /auth/profile     one-time profile creation

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

src/db-migrate.js

@@ -463,6 +463,21 @@ async function migrate() {
       FOR EACH ROW EXECUTE FUNCTION update_updated_at()
   `);
 
+  // Link users_public ↔ users (1:1, app-profile per auth user)
+  await query(`ALTER TABLE users_public ADD COLUMN IF NOT EXISTS user_id UUID`).catch(() => {});
+  await query(`ALTER TABLE users_public ADD CONSTRAINT users_public_user_id_fkey FOREIGN KEY (user_id) REFERENCES users(id) ON DELETE CASCADE`).catch(() => {});
+  await query(`CREATE UNIQUE INDEX IF NOT EXISTS users_public_user_id_idx ON users_public (user_id) WHERE user_id IS NOT NULL`);
+
+  // Seed languages (de exists, add en + sv)
+  await query(`CREATE UNIQUE INDEX IF NOT EXISTS languages_short_en_idx ON languages (short_en) WHERE short_en IS NOT NULL`).catch(() => {});
+  await query(`
+    INSERT INTO languages (short_en, titel_de, titel_en, titel_sv, status, published_at)
+    VALUES
+      ('en', 'Englisch',   'English', 'Engelska', 'published', NOW()),
+      ('sv', 'Schwedisch', 'Swedish', 'Svenska',  'published', NOW())
+    ON CONFLICT (short_en) DO NOTHING
+  `).catch(() => {});
+
   console.log('Migration complete');
 }