fix(workflow): remove build contexts from compose; build.sh uses docker build directly

docker-compose.yml

@@ -4,9 +4,6 @@ services:
   # Enforces an egress allowlist — see proxy/squid.conf.
   proxy:
     image: registry.zeidler.dev/docker/playground/docker-claude-proxy:${IMAGE_TAG:-latest}
-    build:
-      context: proxy
-      dockerfile: Dockerfile
     networks:
       - claude-internal # reachable by claude and webui containers
       - proxy-external # has outbound internet access
@@ -26,9 +23,6 @@ services:
   # Run via "docker compose run --rm --service-ports claude" (managed by claude.sh).
   claude:
     image: registry.zeidler.dev/docker/playground/docker-claude-claude:${IMAGE_TAG:-latest}
-    build:
-      context: claude/
-      dockerfile: Dockerfile
     depends_on:
       proxy:
         condition: service_healthy
@@ -67,9 +61,6 @@ services:
   # Network isolation is identical to the CLI container.
   webui:
     image: registry.zeidler.dev/docker/playground/docker-claude-claude:${IMAGE_TAG:-latest}
-    build:
-      context: claude/
-      dockerfile: Dockerfile
     entrypoint: ["/usr/local/bin/webui-entrypoint.sh"]
     depends_on:
       proxy: