Enable CGo in Dockerfile builder stage

[Copilot]

The builder stage had CGo disabled (CGO_ENABLED=0), which needs to be enabled for builds requiring C interop.

Change

• Dockerfile: Set CGO_ENABLED=1 in the builder RUN step

# Before
RUN CGO_ENABLED=0 GOOS=linux GOARCH=$TARGETARCH go build ...

# After
RUN CGO_ENABLED=1 GOOS=linux GOARCH=$TARGETARCH go build ...

Note: With CGo enabled, the resulting binary is dynamically linked. Verify that the distroless/minimal final stage image provides the required C runtime libraries, or ensure dependencies are statically linked.