Fix Performance page showing empty data

The trends and snapshots endpoints returned periodLabel ("last_30_days")
as the date field, which parseISO() couldn't parse, causing all records
to be filtered out. Now uses capturedAt timestamp for date filtering and
display.

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

apps/api/src/routes/performance.ts

@@ -123,6 +123,7 @@ export default async function (fastify: FastifyInstance) {
       const rows = await db
         .select({
           date: performanceSnapshots.periodLabel,
+          capturedAt: performanceSnapshots.capturedAt,
           platformId: performanceSnapshots.platformId,
           viewsSearch: performanceSnapshots.viewsSearch,
           viewsListing: performanceSnapshots.viewsListing,