Add quick-add watchlist button and consolidate server actions into lib/actions

Move all server actions from scattered page-level files into shared lib/actions/
directory (settings.ts, titles.ts, watchlist.ts) so they can be reused across
the app. Add a hover-triggered plus button on explore page title cards that lets
users add titles to their watchlist without navigating away.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

lib/actions/watchlist.ts

@@ -0,0 +1,39 @@
+"use server";
+
+import { and, eq } from "drizzle-orm";
+import { headers } from "next/headers";
+import { auth } from "@/lib/auth/server";
+import { db } from "@/lib/db/client";
+import { userTitleStatus } from "@/lib/db/schema";
+import { importTitle } from "@/lib/services/metadata";
+import { setTitleStatus } from "@/lib/services/tracking";
+
+export async function quickAddToWatchlist(
+  tmdbId: number,
+  type: "movie" | "tv",
+) {
+  const session = await auth.api.getSession({ headers: await headers() });
+  if (!session) throw new Error("Unauthorized");
+  const userId = session.user.id;
+
+  const title = await importTitle(tmdbId, type);
+  if (!title) throw new Error("Failed to import title");
+
+  const existing = db
+    .select()
+    .from(userTitleStatus)
+    .where(
+      and(
+        eq(userTitleStatus.userId, userId),
+        eq(userTitleStatus.titleId, title.id),
+      ),
+    )
+    .get();
+
+  if (existing) {
+    return { success: true, titleId: title.id, alreadyAdded: true };
+  }
+
+  setTitleStatus(userId, title.id, "watchlist");
+  return { success: true, titleId: title.id, alreadyAdded: false };
+}