Added backend dockerfile

Dockerfile.backend

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+FROM golang:1.24.4-alpine3.22@sha256:68932fa6d4d4059845c8f40ad7e654e626f3ebd3706eef7846f319293ab5cb7a as base
+
+# Set up workdir
+WORKDIR /app
+
+# Install dependencies
+# COPY go.mod go.sum ./
+COPY go.mod ./
+RUN go mod download
+
+# Copy code, and compile 
+COPY . .
+RUN go build -o server main.go
+
+# Expose 8080 port
+EXPOSE 8080
+
+# Run server binary on start
+CMD ["./server"]
+

backend/go.mod

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+module backend
+
+go 1.24.4

backend/main.go

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+package main
+
+import "time"
+
+func main() {
+	println("Hello, world!")
+
+	for {
+		time.Sleep(1 * time.Second)
+	}
+}

caddy/Caddyfile

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+{
+    admin off
+    auto_https off
+}

docker-compose.yml

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+services:
+  backend:
+    build:
+      context: ./backend
+      dockerfile: ../Dockerfile.backend
+
+    container_name: cover-letter-backend
+
+    networks:
+      - cover-letter-network
+
+networks:
+  cover-letter-network:
+    driver: bridge