Harden API input validation, error handling, and optimistic rollbacks

Add try/catch around `request.json()` in all POST routes to return a
400 instead of crashing on malformed bodies. Validate `type` as a
strict `"movie" | "tv"` enum in search, discover, import, and resolve
routes. Validate `tmdbId` as a positive integer. Add a
`SORT_BY_PATTERN` regex and page-range check (1–500) to the discover
route. Wrap all outbound TMDB calls in try/catch and return 502 on
failure so clients get a structured error rather than an unhandled
rejection.

Fix optimistic-update rollbacks in `use-title-actions`: capture
`prevStatus` and `prevWatches` before each mutation and restore both
atoms in the catch block for catchUp, handleMarkSeason,
handleUnmarkSeason, and single-episode toggle.

Fix a bug in `getContinueWatchingFeed` where the watchDateMap could
hold a stale date for episodes watched more than once; the map now
keeps the most-recent `watchedAt` per episode.

app/api/admin/jobs/trigger/route.ts

@@ -12,8 +12,13 @@ export async function POST(request: Request) {
     return NextResponse.json({ error: "Forbidden" }, { status: 403 });
   }
 
-  const body = await request.json();
-  const jobName = body?.jobName;
+  let body: unknown;
+  try {
+    body = await request.json();
+  } catch {
+    return NextResponse.json({ error: "Invalid JSON body" }, { status: 400 });
+  }
+  const jobName = (body as { jobName?: unknown })?.jobName;
 
   if (!jobName || typeof jobName !== "string") {
     return NextResponse.json(