feat(db+auth): add pg pool, admin_users email/provider migration, refactor auth lookup

- Create src/lib/db.ts (shared pg.Pool, query/withTx helpers, server-only)
- Add @types/pg devDep
- Migration 204: add email, auth_provider, auth_subject columns to
  admin_users; backfill from auth.users; new upsert_admin_user accepts
  multi-provider args; new get_admin_user_for_session RPC resolves
  Auth.js session id (UUID or Google sub) to an admin row
- Refactor getAdminUser() to use pg + new RPC; auto-provisions on first
  Google sign-in using session.user.email
- Refactor updatePasswordAction to call update_user_password via pg
  (drops the Supabase REST hop)
- Delete orphaned src/actions/login.ts (replaced by auth-actions.ts)
- Drop remaining DEV_FORCE_UID references in users.ts; dev path now
  uses dev_session cookie (the only cookie the dev flow can set)
- Update AdminUser type: user_id is now string | null (Google users
  have no Supabase auth id); add email + auth_provider fields
- Fix downstream type errors: StopProductAssignment.callerUid accepts
  null; pickup.ts performedBy widens to string | null
- Bump vitest config, tests/, and other earlier cleanup changes

src/components/admin/StopProductAssignment.tsx

@@ -20,7 +20,7 @@ type StopProductAssignmentProps = {
   stopId: string;
   allProducts: Product[];
   assignedProducts: AssignedProduct[];
-  callerUid: string;
+  callerUid: string | null;
 };
 
 export default function StopProductAssignment({

src/components/auth/ClerkComponents.tsx

@@ -1,10 +0,0 @@
-// Auth Components for Clerk
-import { UserButton } from "@clerk/nextjs";
-
-export default function ClerkComponents() {
-  return (
-    <div className="flex items-center gap-4">
-      <UserButton />
-    </div>
-  );
-}

src/components/providers/ClerkProvider.tsx

@@ -1,10 +0,0 @@
-// Clerk Authentication Provider
-import { ClerkProvider } from "@clerk/nextjs";
-
-export default function ClerkAuthProvider({ children }: { children: React.ReactNode }) {
-  return (
-    <ClerkProvider>
-      {children}
-    </ClerkProvider>
-  );
-}