Refactor auth session handling and server actions across app

- Overhaul `lib/auth/server.ts` and `lib/auth/session.ts`; update all API
  routes and server actions to use the revised session pattern
- Refactor server actions (settings, titles, watchlist, setup) for
  consistency with new auth layer
- Extract `SetupForm` into its own client component with `useActionState`,
  animated steps, and copyable env snippets
- Move landing page redirect logic into `app/page.tsx`; slim down
  `LandingPage` component
- Add `proxy.ts` for local dev proxying
- Minor cleanup to `NavBar`, `MobileTabBar`, and `TitleCard`

lib/services/lists.test.ts

@@ -14,8 +14,9 @@ import {
 } from "./lists";
 
 // Mock getTvExternalIds for lazy resolution tests
-const mockGetTvExternalIds = mock(() =>
-  Promise.resolve({ tvdb_id: 55555, imdb_id: "tt9999999" }),
+const mockGetTvExternalIds = mock(
+  (): Promise<{ tvdb_id: number | null; imdb_id: string | null }> =>
+    Promise.resolve({ tvdb_id: 55555, imdb_id: "tt9999999" }),
 );
 mock.module("@/lib/tmdb/client", () => ({
   getTvExternalIds: mockGetTvExternalIds,