feat: add OpenClaw plugin manifest and entry point

- Add openclaw.plugin.json with proper configSchema
- Add index.js as plugin entry point
- Fix plugin id to 'padded-cell' to match manifest

openclaw.plugin.json

@@ -3,7 +3,13 @@
   "name": "PaddedCell",
   "version": "0.1.0",
   "description": "Secure password management, safe execution, and coordinated restart",
-  "entry": "./safe-restart/dist/index.js",
+  "entry": "./index.js",
+  "configSchema": {
+    "type": "object",
+    "properties": {
+      "enabled": { "type": "boolean", "default": true }
+    }
+  },
   "tools": [
     {
       "name": "pcexec",