feat: sitemap remediation, PWA activation, search refinements, Steam Deck UX

Sitemap:
- Switch from ISR (revalidate=3600) to force-dynamic for per-request generation
- Flatten into single app/sitemap.ts with inlined static entries and DB queries
- NULL-safe syncStatus filter: ne(games.syncStatus, 'failed') OR isNull(games.syncStatus)
- Structured JSON logging for generated URLs and DB errors
- Delete lib/sitemap/* helpers and app/api/revalidate-sitemap route
- Add basic vitest coverage for sitemap exports

PWA & Offline:
- Add @serwist/next service worker (webpack build) with runtime caching
- Cache strategies: stale-while-revalidate for game pages, network-first for listings/API,
  cache-first for Steam CDN images
- Offline fallback page (public/offline.html)
- Manifest icons: 192px maskable + 512px any
- Viewport meta with viewport-fit=cover, user-scalable=no
- Apple mobile web app meta tags

Search / Filter Refinements:
- Multi-genre OR support in listing API (comma-separated genres)
- Device-scoped FPS filter (min/max FPS constrained to selected device)
- Client-side URL state sync via router.replace for shareable filtered views
- Initialize filter state from URL params on mount
- Auto-collapse filter panel on saved-filter load
- Fix multi-genre saved filter parsing (comma-separated)

Steam Deck / Touch / Gamepad UX:
- WCAG 2.1 AA touch targets (44x44px) on all filter controls
- .gamepad-focus CSS focus ring for controller navigation
- useGamepadNavigation hook: D-pad/left-stick roving tabindex, A/B/X/Y actions
- Integrate gamepad hook into games page (X=search, Y=toggle filters)

Chore:
- Bump version to 2026.0.97

app/sw.ts

@@ -0,0 +1,80 @@
+import type { PrecacheEntry } from "@serwist/precaching";
+import { CacheFirst, NetworkFirst, StaleWhileRevalidate } from "@serwist/strategies";
+import { ExpirationPlugin } from "@serwist/expiration";
+import { Serwist } from "serwist";
+
+declare global {
+  interface Window {
+    __SW_MANIFEST: (string | PrecacheEntry)[];
+  }
+}
+
+const serwist = new Serwist({
+  precacheEntries: self.__SW_MANIFEST,
+  skipWaiting: true,
+  clientsClaim: true,
+  runtimeCaching: [
+    // Game detail pages: stale-while-revalidate, 24h max age
+    {
+      matcher: /\/game\/[\w-]+$/,
+      handler: new StaleWhileRevalidate({
+        cacheName: "game-pages",
+        plugins: [
+          new ExpirationPlugin({ maxEntries: 200, maxAgeSeconds: 24 * 60 * 60 }),
+        ],
+      }),
+    },
+    // Game listing page: network-first (filters matter)
+    {
+      matcher: /\/games(\?.*)?$/,
+      handler: new NetworkFirst({
+        cacheName: "games-listing",
+        plugins: [
+          new ExpirationPlugin({ maxEntries: 20, maxAgeSeconds: 5 * 60 }),
+        ],
+      }),
+    },
+    // Steam CDN images: cache-first, 30 days
+    {
+      matcher: /^https:\/\/cdn\.akamai\.steamstatic\.com\//,
+      handler: new CacheFirst({
+        cacheName: "steam-images",
+        plugins: [
+          new ExpirationPlugin({ maxEntries: 500, maxAgeSeconds: 30 * 24 * 60 * 60 }),
+        ],
+      }),
+    },
+    // SteamGridDB images: cache-first, 30 days
+    {
+      matcher: /^https:\/\/cdn\d?\.steamgriddb\.com\//,
+      handler: new CacheFirst({
+        cacheName: "steamgrid-images",
+        plugins: [
+          new ExpirationPlugin({ maxEntries: 200, maxAgeSeconds: 30 * 24 * 60 * 60 }),
+        ],
+      }),
+    },
+    // API responses: network-first (live data critical)
+    {
+      matcher: /\/api\//,
+      handler: new NetworkFirst({
+        cacheName: "api-responses",
+        plugins: [
+          new ExpirationPlugin({ maxEntries: 100, maxAgeSeconds: 5 * 60 }),
+        ],
+      }),
+    },
+    // Navigation fallback: offline.html for uncached pages
+    {
+      matcher: ({ request }) => request.mode === "navigate",
+      handler: new NetworkFirst({
+        cacheName: "navigation",
+        plugins: [
+          new ExpirationPlugin({ maxEntries: 50, maxAgeSeconds: 24 * 60 * 60 }),
+        ],
+      }),
+    },
+  ],
+});
+
+serwist.addEventListeners();