feat: add alpine-3.24 build config

Mirror the alpine-3.23 setup across the builder Dockerfile/package,
docker-compose service, Makefile/Justfile targets, and the CI matrix.

builder/docker-compose.yml

@@ -96,6 +96,19 @@ services:
     volumes:
       - /tmp/alpine-323:/tmp/output/alpine-323
       - ./build.sh:/build.sh:ro
+  alpine-324:
+    command: ./build.sh
+    environment:
+      - R_VERSION=${R_VERSION}
+      - R_INSTALL_PATH=${R_INSTALL_PATH}
+      - LOCAL_STORE=/tmp/output
+    build:
+      context: .
+      dockerfile: Dockerfile.alpine-324
+    image: r-builds:alpine-324
+    volumes:
+      - /tmp/alpine-324:/tmp/output/alpine-324
+      - ./build.sh:/build.sh:ro
   debian-10:
     command: ./build.sh
     environment: