Overhaul RSS feed widget: persistence, multi-feed management, search, bookmarks

- Add rss_feeds + rss_items tables with indexes and HN default seed
- Add 5-min background RSS sync loop in monitor.js with 90-day prune
- New /api/rss/feeds route for feed CRUD with immediate fetch on add
- Rewrite /api/rss route with search, feed filter, pagination, read/bookmark PATCH
- Full NewsFeed component rewrite: feed manager, search bar, filter pills,
  read/unread tracking, bookmarks, favicons, auto-refresh with new items badge
- Remove placeholder widget, NewsFeed now spans 4 cols / 3 rows
- Add rss-parser deps to Dockerfile for standalone monitor

app/page.tsx

@@ -14,13 +14,8 @@ export default function Home() {
       {/* Row 1 & 2 (Globe spans 2 rows) */}
       <GlobeCard />
 
-      {/* Row 2 */}
+      {/* Row 2-4: NewsFeed spans 4 cols, 3 rows */}
       <NewsFeed />
-
-      {/* Future widget placeholder to fill grid if needed */}
-      <div className="col-span-1 md:col-span-2 lg:col-span-2 row-span-1 bg-neutral-900/50 border border-neutral-800/50 rounded-xl flex items-center justify-center border-dashed">
-        <span className="text-xs text-neutral-600 font-mono">System Metric Placeholder</span>
-      </div>
     </GridShell>
   );
 }