feat(m3): auth & user management with session, tests, and e2e

- Custom error classes (lib/errors.ts) and signed-cookie session
  (lib/auth/session.ts, HMAC-SHA256, httpOnly+sameSite=lax)
- UserRepository + AuthService (bcrypt hashing, role/status checks,
  register/login/logout/getCurrentUser/updateProfile)
- Auth helpers (getCurrentUser), user validator, API error handler
- API routes: register (auto-login), login, logout, me, PATCH users/me,
  GET admin/migrations (admin-only guard)
- middleware.ts redirects unauthenticated page access to /login
- Screens: login (login/register toggle), profile, dashboard skeleton,
  home redirect
- vitest: exclude e2e specs, setupFiles for SESSION_SECRET
- playwright: run migrate before dev server, set SESSION_SECRET
- Unit tests (UserRepository, AuthService, session), integration
  auth-flow, e2e auth.spec (register/login/logout/protected/401)

playwright.config.ts

@@ -18,9 +18,10 @@ export default defineConfig({
     },
   ],
   webServer: {
-    command: 'npm run dev',
+    command: 'npm run migrate && npm run dev',
     url: 'http://localhost:3000',
-    reuseExistingServer: !process.env.CI,
+    reuseExistingServer: false,
     timeout: 120 * 1000,
+    env: { SESSION_SECRET: 'e2e-secret' },
   },
 });