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/api/stats/route.ts

@@ -1,45 +0,0 @@
-import { NextResponse } from "next/server";
-import { getSession } from "@/lib/auth/session";
-import {
-  getWatchCount,
-  getWatchHistory,
-  type TimePeriod,
-} from "@/lib/services/discovery";
-
-const validTypes = ["movies", "episodes"] as const;
-const validPeriods: TimePeriod[] = [
-  "today",
-  "this_week",
-  "this_month",
-  "this_year",
-];
-
-export async function GET(request: Request) {
-  const session = await getSession();
-  if (!session)
-    return NextResponse.json({ error: "Unauthorized" }, { status: 401 });
-
-  const { searchParams } = new URL(request.url);
-  const type = searchParams.get("type");
-  const period = searchParams.get("period");
-
-  if (
-    !type ||
-    !period ||
-    !validTypes.includes(type as (typeof validTypes)[number]) ||
-    !validPeriods.includes(period as TimePeriod)
-  ) {
-    return NextResponse.json({ error: "Invalid parameters" }, { status: 400 });
-  }
-
-  const typedType = type as "movies" | "episodes";
-  const typedPeriod = period as TimePeriod;
-  const count = getWatchCount(session.user.id, typedType, typedPeriod);
-
-  if (searchParams.get("history") === "true") {
-    const history = getWatchHistory(session.user.id, typedType, typedPeriod);
-    return NextResponse.json({ count, history });
-  }
-
-  return NextResponse.json({ count });
-}