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

.gitignore

@@ -28,3 +28,6 @@ Thumbs.db
 *.a
 *.test
 vendor/
+
+# Lock files (sub-packages)
+plugin/package-lock.json