feat: add Go microservice, Dockerfile, docker-compose, and API submission endpoint

Dockerfile

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+# Stage 1: Build the Go binary
+FROM golang:1.22-alpine AS builder
+
+WORKDIR /app
+
+COPY go.mod ./
+COPY . .
+
+RUN CGO_ENABLED=0 GOOS=linux go build -ldflags="-w -s" -o server .
+
+# Stage 2: Ultra-lightweight runtime container
+FROM alpine:3.19
+
+RUN apk add --no-cache ca-certificates tzdata
+
+WORKDIR /app
+
+# Copy binary and static front-end assets
+COPY --from=builder /app/server /app/server
+COPY --from=builder /app/public /app/public
+
+EXPOSE 8080
+
+ENTRYPOINT ["/app/server"]