feat: switch monitor client to Docker-first runtime

- remove install.sh-based deployment path
- add multi-stage Dockerfile for HarborForge.Monitor
- support HF_MONITER_* env vars and keep HF_MONITOR_* compatibility
- add rootfs-aware host metric collection for Docker deployment

config.example.json

@@ -3,5 +3,6 @@
   "identifier": "vps-01",
   "apiKey": "replace-with-server-api-key",
   "reportIntervalSec": 30,
-  "logLevel": "info"
+  "logLevel": "info",
+  "rootFs": "/host"
 }