feat: refactor project structure + add pcguard + AGENT_VERIFY injection

- Restructure: pcexec/ and safe-restart/ → plugin/{tools,core,commands}
- New pcguard Go binary: validates AGENT_VERIFY, AGENT_ID, AGENT_WORKSPACE
- pcexec now injects AGENT_VERIFY env + appends openclaw bin to PATH
- plugin/index.ts: unified TypeScript entry point with resolveOpenclawPath()
- install.mjs: support --openclaw-profile-path, install pcguard, new paths
- README: updated structure docs + security limitations note
- Removed old root index.js and openclaw.plugin.json

plugin/core/index.ts

@@ -0,0 +1,4 @@
+export { StatusManager, type AgentStatus, type GlobalStatus, type AgentState } from './status-manager';
+export { createApiServer, startApiServer } from './api';
+export { safeRestart, createSafeRestartTool, type SafeRestartOptions, type SafeRestartResult } from './safe-restart';
+export { SlashCommandHandler, type SlashCommandOptions } from '../commands/slash-commands';