[BACKEND] Initialize Go backend structure and dependencies (#23)

Dockerfile.unified

@@ -1,25 +1,28 @@
-# ==========================================
-# Chat Switchboard Unified Dockerfile
-# Option B: Multi-stage build
-# ==========================================
+# ============================================
+# Chat Switchboard - Unified Dockerfile
+# ============================================
+# Stage 1: Build Go backend
+# Stage 2: Build standalone frontend
+# Stage 3: Production image (nginx + backend)
+#
+# nginx serves frontend on :80, proxies /api/ to Go on :8080
+# ============================================
 
-# Stage 1: Backend build
+# ── Stage 1: Go backend build ────────────────
 FROM golang:1.22-bookworm AS backend
 
 WORKDIR /app
 
-COPY server/go.mod ./
-COPY server/go.sum ./
-RUN go mod download
+COPY server/go.mod server/go.sum* ./
+RUN go mod download && go mod verify
 
 COPY server/ .
-RUN CGO_ENABLED=1 go build -o /backend chat-switchboard-api
+RUN CGO_ENABLED=0 go build -ldflags="-s -w" -o /bin/switchboard .
 
-# Stage 2: Frontend build
+# ── Stage 2: Frontend build ──────────────────
 FROM alpine:3.19 AS frontend
 
 WORKDIR /app
-
 RUN apk add --no-cache bash coreutils
 
 COPY build.sh ./
@@ -27,24 +30,22 @@ COPY src ./src
 
 RUN chmod +x build.sh && ./build.sh
 
-# Stage 3: Production
-FROM nginx:alpine AS production
+# ── Stage 3: Production ─────────────────────
+FROM nginx:1-alpine
 
-# Copy backend binary
-COPY --from=backend /backend /usr/local/bin/
+RUN apk add --no-cache bash
 
-# Copy built frontend files
+# Copy Go backend
+COPY --from=backend /bin/switchboard /usr/local/bin/switchboard
+
+# Copy built frontend
 COPY --from=frontend /app/standalone /usr/share/nginx/html
 
-# Copy custom nginx config for reverse proxy
+# Copy nginx config
 COPY nginx.conf /etc/nginx/conf.d/default.conf
 
-# Create startup script
-RUN echo '#!/bin/sh\n\
-mkdir -p /app/data\n\
-/usr/local/bin/backend serve &\n\
-nginx -g "daemon off;"\n' > /start.sh && chmod +x /start.sh
+# Startup script: launches Go backend before nginx starts
+COPY scripts/docker-entrypoint.sh /docker-entrypoint.d/90-start-backend.sh
+RUN chmod +x /docker-entrypoint.d/90-start-backend.sh
 
 EXPOSE 80
-
-CMD ["/start.sh"]