refactor: restructure project layout and add install.mjs

- Move src/ → plugin/ with subdirectories:
  - plugin/core/ (business logic, models, store, permissions, utils, memory)
  - plugin/tools/ (query, resources)
  - plugin/commands/ (placeholder for slash commands)
  - plugin/hooks/ (placeholder for lifecycle hooks)
  - plugin/index.ts (wiring layer only, no business logic)
- Add install.mjs with --install, --uninstall, --openclaw-profile-path
- Add skills/ and docs/ root directories
- Move planning docs (PLAN.md, FEAT.md, AGENT_TASKS.md) to docs/
- Remove old scripts/install.sh
- Update tsconfig rootDir: src → plugin
- Update README.md and README.zh.md with new layout
- Bump version to 0.2.0
- All tests pass

tsconfig.json

@@ -8,9 +8,9 @@
     "forceConsistentCasingInFileNames": true,
     "skipLibCheck": true,
     "outDir": "dist/yonexus",
-    "rootDir": "src",
+    "rootDir": "plugin",
     "declaration": true,
     "types": ["node"]
   },
-  "include": ["src/**/*.ts"]
+  "include": ["plugin/**/*.ts"]
 }