feat: fix SQLite safety in hermes backup + add --quick snapshots + /snapshot command (#8971)

Three changes consolidated into the existing backup system:

1. Fix: hermes backup now uses sqlite3.Connection.backup() for .db files
   instead of raw file copy. Raw copy of a WAL-mode database can produce
   a corrupted backup — the backup() API handles this correctly.

2. hermes backup --quick: fast snapshot of just critical state files
   (config.yaml, state.db, .env, auth.json, cron/jobs.json, etc.)
   stored in ~/.hermes/state-snapshots/. Auto-prunes to 20 snapshots.

3. /snapshot slash command (alias /snap): in-session interface for
   quick state snapshots. create/list/restore/prune subcommands.
   Restore by ID or number. Powered by the same backup module.

No new modules — everything lives in hermes_cli/backup.py alongside
the existing full backup/import code.

No hooks in run_agent.py — purely on-demand, zero runtime overhead.

Closes the use case from PRs #8406 and #7813 with ~200 lines of new
logic instead of a 1090-line content-addressed storage engine.

hermes_cli/main.py

@@ -2848,8 +2848,12 @@ def cmd_config(args):
 
 def cmd_backup(args):
     """Back up Hermes home directory to a zip file."""
-    from hermes_cli.backup import run_backup
-    run_backup(args)
+    if getattr(args, "quick", False):
+        from hermes_cli.backup import run_quick_backup
+        run_quick_backup(args)
+    else:
+        from hermes_cli.backup import run_backup
+        run_backup(args)
 
 
 def cmd_import(args):
@@ -5081,12 +5085,22 @@ Examples:
         "backup",
         help="Back up Hermes home directory to a zip file",
         description="Create a zip archive of your entire Hermes configuration, "
-                    "skills, sessions, and data (excludes the hermes-agent codebase)"
+                    "skills, sessions, and data (excludes the hermes-agent codebase). "
+                    "Use --quick for a fast snapshot of just critical state files."
     )
     backup_parser.add_argument(
         "-o", "--output",
         help="Output path for the zip file (default: ~/hermes-backup-<timestamp>.zip)"
     )
+    backup_parser.add_argument(
+        "-q", "--quick",
+        action="store_true",
+        help="Quick snapshot: only critical state files (config, state.db, .env, auth, cron)"
+    )
+    backup_parser.add_argument(
+        "-l", "--label",
+        help="Label for the snapshot (only used with --quick)"
+    )
     backup_parser.set_defaults(func=cmd_backup)
 
     # =========================================================================