Fix ssh from host not working in docker

docker-compose.yml

@@ -1,6 +1,27 @@
 services:
   apparel-designer:
-    build: { context: ., dockerfile: Dockerfile }
+    build:
+      context: .
+      dockerfile: Dockerfile
+      # Forward the host's SSH agent into the build. Needed because
+      # the `goods-editor` npm dependency uses a git+ssh: URL, so
+      # `npm install` has to authenticate against git.kadil.dev
+      # during the build. "default" means "use the SSH_AUTH_SOCK
+      # environment variable on the host" — matches the build
+      # command `docker build --ssh default`.
+      #
+      # The host running `docker compose build` must have:
+      #   • An ssh-agent running with the right key loaded
+      #     (verify with `ssh-add -l`).
+      #   • Docker 23+ (BuildKit is the default; older versions
+      #     need `DOCKER_BUILDKIT=1` exported).
+      #
+      # No SSH material is baked into the image — the agent is only
+      # available during the single RUN step in the Dockerfile that
+      # has `--mount=type=ssh`. See the Dockerfile docblock for the
+      # full mechanism.
+      ssh:
+        - default
     container_name: apparel-designer
     ports: ["3001:3001"]
     volumes: