feat: add fix-inconsistencies library maintenance tool

[tankxbvr]

Adds a Fix All button under Options → Cache that scans for library data that has drifted out of sync and repairs it in the background (with live progress):

• Files matched to a deleted or missing scene — re-matched to a live scene of the same title (e.g. a re-published version), or unmatched.
• Scenes whose is_available / is_accessible / total_file_size no longer match their files — recomputed.
• Tags / actors whose cached scene counts are stale — recounted.

The scan and fixes are exposed under /api/inconsistencies in a self-contained pkg/inconsistencies package. This repairs existing drift; the root-cause prevention lives in the related fixes to UpdateStatus and CountTags/CountActorTags.