Update Dockerfile

Dockerfile

@@ -3,13 +3,14 @@ FROM golang:1.21-alpine AS builder
 
 WORKDIR /app
 
-# Copy mod files and download dependencies
+# Copy source code and mod files
 COPY go.mod ./
-RUN go mod tidy
-
-# Copy the source code
 COPY main.go .
 
+# Download dependencies
+# Note: main.go must be present for 'go mod tidy' to detect imports correctly
+RUN go mod tidy
+
 # Build the application
 # CGO_ENABLED=0 ensures a static binary
 RUN CGO_ENABLED=0 GOOS=linux go build -o ctf-server main.go