feat: add 'hermes claw migrate' command + migration docs

- Add hermes_cli/claw.py with full CLI migration handler:
  - hermes claw migrate (interactive migration with confirmation)
  - --dry-run, --preset, --overwrite, --skill-conflict flags
  - --source for custom OpenClaw path
  - --yes to skip confirmation
  - Clean formatted output matching setup wizard style

- Fix Python 3.11+ @dataclass compatibility bug in dynamic module loading:
  - Register module in sys.modules before exec_module()
  - Fixes both setup.py (PR #981) and new claw.py

- Add 16 tests in tests/hermes_cli/test_claw.py covering:
  - Script discovery (project root, installed, missing)
  - Command routing
  - Dry-run, execute, cancellation, error handling
  - Preset/secrets behavior, report formatting

- Documentation updates:
  - README.md: Add 'hermes claw migrate' to Getting Started, new Migration section
  - docs/migration/openclaw.md: Full migration guide with all options
  - SKILL.md: Add CLI Command section at top of openclaw-migration skill

hermes_cli/setup.py

@@ -2074,7 +2074,15 @@ def _offer_openclaw_migration(hermes_home: Path) -> bool:
             return False
 
         mod = importlib.util.module_from_spec(spec)
-        spec.loader.exec_module(mod)
+        # Register in sys.modules so @dataclass can resolve the module
+        # (Python 3.11+ requires this for dynamically loaded modules)
+        import sys as _sys
+        _sys.modules[spec.name] = mod
+        try:
+            spec.loader.exec_module(mod)
+        except Exception:
+            _sys.modules.pop(spec.name, None)
+            raise
 
         # Run migration with the "full" preset, execute mode, no overwrite
         selected = mod.resolve_selected_options(None, None, preset="full")