Persist dashboard periods and explore genre filters in URL via nuqs

- Add `nuqs` dependency; define `dashboardSearchParams` and
  `exploreSearchParams` loaders in new `search-params.ts` files
- Thread `moviePeriod`/`episodePeriod` from URL into `StatsSection`
  and `StatsDisplay`, replacing local `useState` with `useQueryStates`
- Rename `getUserStats` fields `moviesThisMonth`/`episodesThisWeek` →
  `movieCount`/`episodeCount` and accept period args so SSR stats
  match the active URL params
- Pre-fetch genre-filtered results server-side on the explore page
  when `movieGenre`/`tvGenre` params are present; pass as
  `initialGenreItems` to `FilterableTitleRow` so first paint is
  already populated
- Render genre chips as `<Link>` elements (with click-handler
  fallback) so genre selections produce shareable, bookmarkable URLs

lib/services/discovery.ts

@@ -144,15 +144,19 @@ export function getWatchHistory(
 }
 
 export interface DashboardStats {
-  moviesThisMonth: number;
-  episodesThisWeek: number;
+  movieCount: number;
+  episodeCount: number;
   librarySize: number;
   completed: number;
 }
 
-export function getUserStats(userId: string): DashboardStats {
-  const moviesThisMonth = getWatchCount(userId, "movies", "this_month");
-  const episodesThisWeek = getWatchCount(userId, "episodes", "this_week");
+export function getUserStats(
+  userId: string,
+  moviePeriod: TimePeriod = "this_month",
+  episodePeriod: TimePeriod = "this_week",
+): DashboardStats {
+  const movieCount = getWatchCount(userId, "movies", moviePeriod);
+  const episodeCount = getWatchCount(userId, "episodes", episodePeriod);
 
   const [statusCounts] = db
     .select({
@@ -164,8 +168,8 @@ export function getUserStats(userId: string): DashboardStats {
     .all();
 
   return {
-    moviesThisMonth,
-    episodesThisWeek,
+    movieCount,
+    episodeCount,
     librarySize: statusCounts?.librarySize ?? 0,
     completed: statusCounts?.completed ?? 0,
   };