[Console] Batch delete expired application backups in cleanup task

[shangeyao]

Problem

ApplicationBackUpCleanTask performs N+1 queries: one grouped query per app id, then loads all backups per app and deletes them one-by-one with removeById.

Proposed solution

• Load all backups in a single query
• Group and trim in memory per application id
• Delete expired records with one removeByIds batch call

[shangeyao]

Closing because related PR #4391 was closed without merge. Console frontend is being refactored; this work is deferred.