Add automatic plugin installation on first Docker deployment

- Add docker-entrypoint.sh: runs migrations and bootstraps plugins
- Add bootstrap-plugins.sh: installs all plugins (disabled by default)
- Update Dockerfile to use entrypoint
- Plugins can now be enabled via Settings UI after first deployment
- Idempotent: safe to run multiple times
- Solves issue where imported prod databases had tables but no plugin registry

Dockerfile

@@ -123,6 +123,9 @@ COPY migrations/ ./migrations/
 COPY scripts/ ./scripts/
 COPY wsgi.py ./
 
+# Make entrypoint and bootstrap scripts executable
+RUN chmod +x /app/scripts/docker-entrypoint.sh /app/scripts/bootstrap-plugins.sh
+
 # Built SPA from stage 1. Flask serves it via register_frontend_routes.
 COPY --from=frontendbuild /build/frontend/dist ./frontend/dist
 
@@ -139,6 +142,9 @@ USER shopdb
 
 EXPOSE 5001
 
+# Entrypoint runs migrations and bootstraps plugins on first deployment
+ENTRYPOINT ["/app/scripts/docker-entrypoint.sh"]
+
 # Probe the public health route, not the login endpoint. Probing POST
 # /api/auth/login logged a 400 every 30s and ran the credential path from a
 # health check. The route answers 200 even when the database is degraded, so the