Add Go VPN admin panel with Docker Compose and Postgres 17.

Co-authored-by: Cursor <cursoragent@cursor.com>

Dockerfile

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+FROM golang:1.23-alpine AS builder
+
+WORKDIR /src
+RUN apk add --no-cache git ca-certificates
+
+COPY go.mod go.sum ./
+RUN go mod download
+
+COPY . .
+RUN CGO_ENABLED=0 GOOS=linux go build -ldflags="-s -w" -o /out/panel ./cmd/server
+
+FROM alpine:3.21
+RUN apk add --no-cache ca-certificates tzdata
+WORKDIR /app
+
+COPY --from=builder /out/panel /app/panel
+COPY web /app/web
+
+ENV APP_PORT=8080
+EXPOSE 8080
+
+CMD ["/app/panel"]