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`

app/api/backup/[filename]/route.ts

@@ -1,14 +1,13 @@
 import path from "node:path";
-import { headers } from "next/headers";
 import { type NextRequest, NextResponse } from "next/server";
-import { auth } from "@/lib/auth/server";
+import { getSession } from "@/lib/auth/session";
 import { getBackupPath } from "@/lib/services/backup";
 
 export async function GET(
   _req: NextRequest,
   { params }: { params: Promise<{ filename: string }> },
 ) {
-  const session = await auth.api.getSession({ headers: await headers() });
+  const session = await getSession();
   if (!session) {
     return NextResponse.json({ error: "Unauthorized" }, { status: 401 });
   }

app/api/backup/restore/route.ts

@@ -1,12 +1,11 @@
-import { headers } from "next/headers";
 import { NextResponse } from "next/server";
-import { auth } from "@/lib/auth/server";
+import { getSession } from "@/lib/auth/session";
 import { restoreFromBackup } from "@/lib/services/backup";
 
 const MAX_SIZE = 500 * 1024 * 1024; // 500MB
 
 export async function POST(req: Request) {
-  const session = await auth.api.getSession({ headers: await headers() });
+  const session = await getSession();
   if (!session) {
     return NextResponse.json({ error: "Unauthorized" }, { status: 401 });
   }