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

Dockerfile

@@ -0,0 +1,20 @@
+FROM golang:1.22-alpine AS builder
+WORKDIR /src
+COPY go.mod go.sum ./
+RUN go mod download
+COPY . .
+RUN CGO_ENABLED=0 GOOS=linux GOARCH=amd64 go build -o /out/harborforge-monitor ./cmd/harborforge-monitor
+
+FROM alpine:3.20
+RUN apk add --no-cache ca-certificates tzdata
+WORKDIR /app
+COPY --from=builder /out/harborforge-monitor /usr/local/bin/harborforge-monitor
+
+ENV HF_MONITER_BACKEND_URL=https://monitor.hangman-lab.top \
+    HF_MONITER_IDENTIFIER= \
+    HF_MONITER_API_KEY= \
+    HF_MONITER_REPORT_INTERVAL=30 \
+    HF_MONITER_LOG_LEVEL=info \
+    HF_MONITER_ROOTFS=/host
+
+ENTRYPOINT ["/usr/local/bin/harborforge-monitor"]