feat: add MONITOR_PORT env var and monitorPort config field

- Added MonitorPort field to Config struct (TODO 5.1)
- Config loads from MONITOR_PORT or HF_MONITOR_PORT env vars
- Added to Dockerfile env defaults
- Updated config.example.json
- Merge function handles monitorPort from file config

Prepares Monitor for local plugin communication bridge (TODO 5.1, 5.2)

Dockerfile

@@ -15,6 +15,7 @@ ENV HF_MONITER_BACKEND_URL=https://monitor.hangman-lab.top \
     HF_MONITER_API_KEY= \
     HF_MONITER_REPORT_INTERVAL=30 \
     HF_MONITER_LOG_LEVEL=info \
-    HF_MONITER_ROOTFS=/host
+    HF_MONITER_ROOTFS=/host \
+    MONITOR_PORT=0
 
 ENTRYPOINT ["/usr/local/bin/harborforge-monitor"]

config.example.json

@@ -4,5 +4,6 @@
   "apiKey": "replace-with-server-api-key",
   "reportIntervalSec": 30,
   "logLevel": "info",
-  "rootFs": "/host"
+  "rootFs": "/host",
+  "monitorPort": 0
 }

internal/config/config.go

@@ -14,6 +14,7 @@ type Config struct {
 	ReportIntervalSec int    `json:"reportIntervalSec"`
 	LogLevel          string `json:"logLevel"`
 	RootFS            string `json:"rootFs"`
+	MonitorPort       int    `json:"monitorPort"`
 }
 
 func Load(path string) (Config, error) {
@@ -43,6 +44,7 @@ func Load(path string) (Config, error) {
 	cfg.ReportIntervalSec = getenvIntAny([]string{"HF_MONITER_REPORT_INTERVAL", "HF_MONITOR_REPORT_INTERVAL"}, cfg.ReportIntervalSec)
 	cfg.LogLevel = getenvAny([]string{"HF_MONITER_LOG_LEVEL", "HF_MONITOR_LOG_LEVEL"}, cfg.LogLevel)
 	cfg.RootFS = getenvAny([]string{"HF_MONITER_ROOTFS", "HF_MONITOR_ROOTFS"}, cfg.RootFS)
+	cfg.MonitorPort = getenvIntAny([]string{"MONITOR_PORT", "HF_MONITOR_PORT"}, cfg.MonitorPort)
 
 	if cfg.BackendURL == "" {
 		return cfg, fmt.Errorf("backendUrl is required")
@@ -88,6 +90,9 @@ func merge(dst *Config, src Config) {
 	if src.RootFS != "" {
 		dst.RootFS = src.RootFS
 	}
+	if src.MonitorPort > 0 {
+		dst.MonitorPort = src.MonitorPort
+	}
 }
 
 func getenvAny(keys []string, fallback string) string {