Migrate authentication to Better Auth

Replace the hand-rolled JWT auth with Better Auth 1.6.25 httpOnly cookie
sessions, validated against the database on every request so revocation,
bans and role changes take effect immediately.

Backend:
- betterAuth.ts wires the Drizzle adapter, magic links, Google sign-in and
  the admin plugin; auth-schema.ts maps Better Auth's models onto the
  existing `users` table so user IDs and their foreign keys survive intact.
- routes/auth.ts is gone; Better Auth serves the standard endpoints and
  authExt.ts carries the flows it doesn't cover.
- auth.ts shrinks to session resolution and helpers; sessions/revocation in
  dashboard.ts now read and delete `auth_sessions` rows directly.
- Schema adds the Better Auth core + admin columns (email_verified, image,
  banned, ban_reason, ban_expires), with migrations and tests.
- rateLimit.ts resolves client IPs spoof-resistantly: proxy headers are only
  honoured from loopback/RFC1918 peers plus TRUSTED_PROXIES.
- passwordPolicy.ts centralises password validation.
- Bump drizzle-orm, drizzle-kit and better-sqlite3 to versions compatible
  with Better Auth.

Frontend:
- auth-client.ts plus a reworked AuthContext and api/client.ts move to
  cookie-based sessions; no more bearer tokens in requests or middleware.

photo-api:
- Validate Better Auth session cookies against the shared auth_sessions
  table instead of verifying JWTs; JWT_SECRET is no longer needed for user
  auth, and PHOTO_VIEW_SECRET now signs gallery view tokens.

BETTER_AUTH_SECRET and BETTER_AUTH_URL are required in production; the
deprecated JWT_SECRET stays only as the photo-api view-token fallback.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

frontend/src/app/(public)/dashboard/page.tsx

@@ -23,7 +23,7 @@ type Tab = 'overview' | 'tickets' | 'payments' | 'account';
 export default function DashboardPage() {
   const router = useRouter();
   const { locale } = useLanguage();
-  const { user, isLoading: authLoading, token } = useAuth();
+  const { user, isLoading: authLoading } = useAuth();
 
   const [activeTab, setActiveTab] = useState<Tab>('overview');
   const [nextEvent, setNextEvent] = useState<NextEventInfo | null>(null);
@@ -36,11 +36,13 @@ export default function DashboardPage() {
       router.push('/login');
       return;
     }
-    if (user && token) {
+    // Auth rides on the httpOnly session cookie; once the user has resolved
+    // the API calls are authenticated automatically.
+    if (user) {
       loadDashboardData();
     }
     // eslint-disable-next-line react-hooks/exhaustive-deps
-  }, [user, authLoading, token]);
+  }, [user, authLoading]);
 
   const loadDashboardData = async () => {
     setLoading(true);