fix(dockerfile): alpine version mismatch between builder and final image

The builder stage uses golang:1.24.0-alpine3.21 but the final image uses alpine:3.19. They should use the same Alpine version to avoid potential compatibility issues. The final image should be updated to alpine:3.21 to match.

Open the Dockerfile and compare the Alpine versions used by the builder and final image stages. Update the final image to Alpine 3.21 to match the builder, then build the image to confirm the stages use compatible versions.

Written by the indexing model from the issue text.