feat: add post-migration cleanup for OpenClaw directories (#4100)

After migrating from OpenClaw, leftover workspace directories contain
state files (todo.json, sessions, logs) that confuse the agent — it
discovers them and reads/writes to stale locations instead of the
Hermes state directory, causing issues like cron jobs reading a
different todo list than interactive sessions.

Changes:
- hermes claw migrate now offers to archive the source directory after
  successful migration (rename to .pre-migration, not delete)
- New `hermes claw cleanup` subcommand for users who already migrated
  and need to archive leftover OpenClaw directories
- Migration notes updated with explicit cleanup guidance
- 42 tests covering all new functionality

Reported by SteveSkedasticity — multiple todo.json files across
~/.hermes/, ~/.openclaw/workspace/, and ~/.openclaw/workspace-assistant/
caused cron jobs to read from wrong locations.

hermes_cli/main.py

@@ -4712,6 +4712,28 @@ For more help on a command:
         help="Skip confirmation prompts"
     )
 
+    # claw cleanup
+    claw_cleanup = claw_subparsers.add_parser(
+        "cleanup",
+        aliases=["clean"],
+        help="Archive leftover OpenClaw directories after migration",
+        description="Scan for and archive leftover OpenClaw directories to prevent state fragmentation"
+    )
+    claw_cleanup.add_argument(
+        "--source",
+        help="Path to a specific OpenClaw directory to clean up"
+    )
+    claw_cleanup.add_argument(
+        "--dry-run",
+        action="store_true",
+        help="Preview what would be archived without making changes"
+    )
+    claw_cleanup.add_argument(
+        "--yes", "-y",
+        action="store_true",
+        help="Skip confirmation prompts"
+    )
+
     def cmd_claw(args):
         from hermes_cli.claw import claw_command
         claw_command(args)