feat(mcp): Steward's own backups: the runs, the next one, checking and making one (#5836)

list_backups, check_backup and make_backup are Settings → Backups for an
agent, admin only like the page. make_backup runs the page's job in the
background and is audited as "<user> via MCP". Restoring stays in the
browser. get_overview names a scheduled backup that failed, is two hours
past its slot, or has no bucket.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

docs/core/backups.md

@@ -80,6 +80,11 @@ While backups are on, Steward records two metrics under the source
 A rule such as `backup_age_secs > 93600` (26 hours) fires when a daily backup
 has been missed.
 
+An agent on the MCP sees the same without a rule. `get_overview` names a
+scheduled backup that failed, is two hours past its slot with none made, or has
+no bucket set up. `list_backups`, `check_backup` and `make_backup` are this
+page's admin tools (see [MCP](mcp.md)); restoring isn't among them.
+
 ## Checking a backup
 
 **Settings → Backups → Check** compares a backup with what is in place, without