Replace API route handlers with server actions across the app

- Delete 10 API routes (stats, system-health, update-check, jobs/trigger,
  backup/restore, person, titles import/resolve, registration/status) and
  move logic into server actions in lib/actions/settings.ts and
  lib/actions/watchlist.ts
- Refactor SystemHealthCards to accept initialData prop and hydrate Jotai
  atoms via useHydrateAtoms; replace useSystemHealth SWR hook with a
  lightweight useSystemHealthRefresh that calls getSystemHealthAction
- Convert BackupRestoreSection to use restoreBackupAction + useTransition
  instead of a raw fetch call
- Split SystemStatusCard, BackgroundJobsCard, and StorageCard into
  standalone components reading from systemHealthDataAtom
- Make SetupPage async with connection() to opt into dynamic rendering

app/(auth)/setup/page.tsx

@@ -1,8 +1,10 @@
 import { redirect } from "next/navigation";
+import { connection } from "next/server";
 import { isTmdbConfigured } from "@/lib/config";
 import { SetupForm } from "./_components/setup-form";
 
-export default function SetupPage() {
+export default async function SetupPage() {
+  await connection();
   if (isTmdbConfigured()) redirect("/");
   return <SetupForm />;
 }