feat(arch): unify frontend and backend into single Go backend server with static export

- Configure Next.js static export (output: 'export') with client-side dynamic fetching
- Implement Go static serving with SPA fallback in backend/internal/router/router.go
- Unify multi-stage build in backend/Dockerfile (Node -> Go -> minimal Alpine runtime)
- Simplify root docker-compose.yml to single anl-app service on port 8080
- Update REQUIREMENTS.md DM-03 and AC-17 normative contracts to v3.0 Unified Go Backend
- Restore strict regression verification in Gate 9 (AC-35/36/37) and unittest suite
- All Go unit tests, TypeScript type checks, ESLint, and E2E gates passed clean

backend/Dockerfile

@@ -1,51 +1,47 @@
 # ==============================================================================
-# Stage 1: Build the Go Binaries
+# Stage 1: Build the static frontend export
 # ==============================================================================
-FROM golang:1.26-alpine AS builder
+FROM node:20-alpine AS frontend-builder
+WORKDIR /app/frontend
+RUN apk add --no-cache libc6-compat
+COPY refer_landing_page/package.json refer_landing_page/package-lock.json ./
+RUN npm ci
+COPY refer_landing_page/ .
+ARG NEXT_PUBLIC_API_BASE_URL=""
+ENV NEXT_PUBLIC_API_BASE_URL=${NEXT_PUBLIC_API_BASE_URL} \
+    NEXT_TELEMETRY_DISABLED=1 \
+    NODE_ENV=production
+RUN npm run build
 
+# ==============================================================================
+# Stage 2: Build the Go binaries
+# ==============================================================================
+FROM golang:1.26-alpine AS backend-builder
 WORKDIR /app
-
-# Install git and certificates
 RUN apk add --no-cache git ca-certificates tzdata
-
-# Download dependencies
-COPY go.mod go.sum ./
+COPY backend/go.mod backend/go.sum ./
 RUN go mod download
-
-# Copy backend source code
-COPY . .
-
-# Build pure-Go static binaries
+COPY backend/ .
 RUN CGO_ENABLED=0 GOOS=linux go build -ldflags="-w -s" -o /bin/api ./cmd/api && \
     CGO_ENABLED=0 GOOS=linux go build -ldflags="-w -s" -o /bin/seed ./cmd/seed && \
     CGO_ENABLED=0 GOOS=linux go build -ldflags="-w -s" -o /bin/export-content ./cmd/export-content
 
 # ==============================================================================
-# Stage 2: Minimal Runtime Image
+# Stage 3: Minimal Alpine runtime — single container, single process
 # ==============================================================================
 FROM alpine:3.20
-
 WORKDIR /app
-
-# Install ca-certificates and sqlite cli for maintenance
 RUN apk add --no-cache ca-certificates tzdata sqlite curl && \
     addgroup -S appgroup && adduser -S appuser -G appgroup
-
-# Create persistent database storage directory
 RUN mkdir -p /app/data && chown -R appuser:appgroup /app/data
 
-# Copy built binaries from builder
-COPY --from=builder /bin/api /app/bin/api
-COPY --from=builder /bin/seed /app/bin/seed
-COPY --from=builder /bin/export-content /app/bin/export-content
+COPY --from=backend-builder /bin/api /app/bin/api
+COPY --from=backend-builder /bin/seed /app/bin/seed
+COPY --from=backend-builder /bin/export-content /app/bin/export-content
+COPY --from=backend-builder /app/seed /app/seed
+COPY --from=backend-builder /app/.env.example /app/.env
+COPY --from=frontend-builder --chown=appuser:appgroup /app/frontend/out /app/web
 
-# Copy seed data
-COPY --from=builder /app/seed /app/seed
-
-# Copy environment template
-COPY --from=builder /app/.env.example /app/.env
-
-# Set environment defaults for container
 ENV HOST=0.0.0.0 \
     PORT=8080 \
     DB_PATH=/app/data/anl.db \
@@ -54,7 +50,6 @@ ENV HOST=0.0.0.0 \
     AUTO_MIGRATE=true
 
 EXPOSE 8080
-
 USER appuser
 
 HEALTHCHECK --interval=30s --timeout=3s --start-period=5s --retries=3 \