Fix RSS time filters and add draggable grid layout

Normalize pub_date to ISO 8601 on insert so SQLite datetime comparisons
work correctly. Migrate existing RFC 2822 dates. Change 1h filter to 12h.
Add react-grid-layout with persistent drag/resize and reset button.

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

app/api/rss/route.ts

@@ -30,7 +30,7 @@ export async function GET(req: NextRequest) {
     }
     if (since) {
         const sinceMap: Record<string, string> = {
-            '1h': '-1 hours',
+            '12h': '-12 hours',
             '24h': '-24 hours',
             '7d': '-7 days',
             '30d': '-30 days',