fix(docker): stop ignoring plugins/ in image build; dev-friendly compose

.dockerignore excluded plugins/ (leftover from the separate-repo era), so the
Dockerfile's COPY plugins/ found nothing and the build failed. Track it now that
first-party plugins ship in the image.

docker-compose.yml reworked for local dev: live-mounted ./steward + ./plugins
with PYTHONPATH=/app, --debug auto-reload, fixed dev SECRET_KEY, Postgres port
exposed, and the host-specific traefik/docker.sock mounts commented out.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

.dockerignore

@@ -26,8 +26,9 @@ config.yaml
 # Runtime data (mounted at runtime via volume)
 playbook_cache/
 
-# Plugins (mounted at runtime via volume)
-plugins/
+# NOTE: first-party plugins under plugins/ now ship IN the image
+# (Dockerfile `COPY plugins/`), so plugins/ must NOT be ignored here.
+# Third-party plugins are mounted at runtime into /data/plugins instead.
 
 # Deployment files not needed in image
 docker-compose.yml