Replace server actions with API routes and add SWR data-fetching hooks

- Convert discover, stats, status, and system-health server actions to
  proper API route handlers under `app/api/`; delete `lib/actions/explore.ts`,
  `lib/actions/settings.ts`, and `lib/actions/setup.ts`
- Add `use-discover`, `use-stats`, and `use-system-health` SWR hooks
  that call the new routes; update `command-palette`, `title-card`,
  `update-toast`, and `stats-display` to consume them
- Lift auth centering wrapper from individual login/register pages into
  `(auth)/layout.tsx`; switch both pages from `auth.api.getSession` to
  the cached `getSession()` helper
- Relocate setup wizard from `app/(auth)/setup/` to `app/setup/` (outside
  auth group) with dedicated `copy-button` and `refresh-button` client
  components
- Move `not-found.tsx` and `error.tsx` to app root so they apply
  globally instead of only within the pages route group

app/api/stats/route.ts

@@ -0,0 +1,34 @@
+import { type NextRequest, NextResponse } from "next/server";
+import { z } from "zod";
+import { getSession } from "@/lib/auth/session";
+import { getWatchCount, getWatchHistory } from "@/lib/services/discovery";
+
+const paramsSchema = z.object({
+  type: z.enum(["movies", "episodes"]),
+  period: z.enum(["today", "this_week", "this_month", "this_year"]),
+});
+
+export async function GET(req: NextRequest) {
+  const session = await getSession();
+  if (!session) {
+    return NextResponse.json({ error: "Unauthorized" }, { status: 401 });
+  }
+
+  const parsed = paramsSchema.safeParse({
+    type: req.nextUrl.searchParams.get("type"),
+    period: req.nextUrl.searchParams.get("period"),
+  });
+
+  if (!parsed.success) {
+    return NextResponse.json(
+      { error: "Invalid type or period parameter" },
+      { status: 400 },
+    );
+  }
+
+  const { type, period } = parsed.data;
+  const count = getWatchCount(session.user.id, type, period);
+  const history = getWatchHistory(session.user.id, type, period);
+
+  return NextResponse.json({ count, history });
+}