Add Docker support: Dockerfile, docker-compose, GitHub Actions

backend/Dockerfile

@@ -2,13 +2,16 @@ FROM golang:1.21-alpine AS builder
 
 WORKDIR /app
 
-RUN apk add --no-cache git
+RUN apk add --no-cache git nodejs npm
 
 COPY go.mod go.sum ./
 RUN go mod download
 
 COPY . .
 
+RUN npm ci --prefix frontend
+RUN npm run build --prefix frontend
+
 RUN CGO_ENABLED=0 GOOS=linux go build -o /app/server ./cmd/server
 
 FROM alpine:latest
@@ -18,6 +21,7 @@ WORKDIR /app
 RUN apk add --no-cache ca-certificates tzdata
 
 COPY --from=builder /app/server .
+COPY --from=builder /app/frontend/dist ./static
 COPY --from=builder /app/uploads ./uploads
 
 EXPOSE 8080