Optimize database queries: add indexes, batch cron scans, transactional writes

Add covering indexes for recommendation rank ordering, title staleness scans,
and type+status filtering. Replace N+1 per-row staleness checks in cron jobs
with set-based batch queries. Wrap availability refresh in a transaction for
atomicity. Batch episode stills query and use existence check instead of
loading all rows for count.

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

drizzle/20260306204637_rare_northstar/migration.sql

@@ -0,0 +1,3 @@
+CREATE INDEX `titleRecommendations_titleId_rank` ON `titleRecommendations` (`titleId`,`rank`);--> statement-breakpoint
+CREATE INDEX `titles_lastFetchedAt` ON `titles` (`lastFetchedAt`);--> statement-breakpoint
+CREATE INDEX `titles_type_status_lastFetchedAt` ON `titles` (`type`,`status`,`lastFetchedAt`);