build: integrate frontend build into Nginx Dockerfile, remove separate frontend image

infrastructure/nginx/Dockerfile

@@ -1,9 +1,21 @@
+# Stage 1: Build frontend
+FROM node:20-alpine AS builder
+WORKDIR /build
+COPY frontend/package*.json ./
+RUN npm ci
+COPY frontend/ .
+RUN npm run build
+
+# Stage 2: Nginx with bundled frontend
 FROM nginx:alpine
 
-COPY nginx.conf /etc/nginx/nginx.conf
+COPY infrastructure/nginx/nginx.conf /etc/nginx/nginx.conf
 
-# Create directories for HLS and frontend
-RUN mkdir -p /srv/frontend /srv/hls /srv/frontend/admin
+# Copy prebuilt frontend from builder stage
+COPY --from=builder /build/dist/ /srv/frontend/
+
+# Create HLS directory
+RUN mkdir -p /srv/hls
 
 EXPOSE 80
 CMD ["nginx", "-g", "daemon off;"]