chore: convert plugin to ESM and migrate to current openclaw plugin SDK

ESM conversion:
- package.json: add "type": "module"; drop stale "main": "index.ts"
- tsconfig.json: switch module/moduleResolution to "nodenext"
- plugin/index.ts: replace `module.exports = { register }` and
  `module.exports.X = X` with `export default definePluginEntry({ ... })`
  plus named ESM re-exports; replace `require('os')`/`require('path')`
  with proper imports.
- plugin/tools/pcexec.ts: replace `require('child_process')` with import
  from "node:child_process".
- plugin/commands/ego-mgr-slash.ts: replace `require('path')` with
  proper path import.
- All relative imports/exports across plugin/ now carry .js extensions
  as required by Node ESM (nodenext module resolution).

Plugin SDK convention update:
- Wrap default export with definePluginEntry({ id, name, description,
  register }) per the current openclaw authoring contract.
- Type api parameter as OpenClawPluginApi (was `any`); the non-standard
  api.registerSlashCommand call is preserved behind a guarded any-cast,
  so the plugin remains a no-op for slash commands when the host doesn't
  expose that hook (matches the previous defensive guard).
- Add openclaw as a devDependency (file:/usr/lib/node_modules/openclaw)
  so tsc can resolve openclaw/plugin-sdk/* subpath types at build time.
- Modernize openclaw.plugin.json: drop entry/version, add
  activation.onStartup so gateway_start fires for this plugin at boot,
  declare contracts.tools listing pcexec/proxy-pcexec/safe_restart.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

plugin/core/api.ts

@@ -1,5 +1,5 @@
 import express from 'express';
-import { StatusManager } from './status-manager';
+import { StatusManager } from './status-manager.js';
 
 export interface ApiOptions {
   port?: number;