Add five endpoints matching the existing backup API pattern:
- GET /snapshots — list with pagination
- POST /snapshot — create (content_types, description)
- POST /snapshot/:id/restore — restore (mode, content_types)
- DELETE /snapshot/:id — delete record + file
- GET /snapshot/:id/download — stream JSON file
ACL: mokosuitebackup.snapshot.manage for write ops, core.manage for read.
Routes registered in webservices plugin alongside backup routes.
Closes#54
After archive is created and checksum computed, automatically verify:
- Archive opens without error
- Contains at least one entry
- database.sql present when backup type includes database
- First entry is readable (spot-check)
Applied to both BackupEngine and SteppedBackupEngine. Throws
RuntimeException on verification failure (backup marked as failed).
Closes#65