rework: address review feedback on PR #126

Changes per sneak's review:
- Delete docker-compose.yml, add example stanza to README
- Define custom domain types: ImageID, ContainerID, UnparsedURL
- Use custom types in all function signatures throughout codebase
- Restore imageID parameter (as domain.ImageID) in deploy pipeline
- buildContainerOptions now takes ImageID directly instead of
  constructing image tag from deploymentID
- Fix pre-existing JS formatting (prettier)

make check passes with zero failures.

README.md

@@ -176,6 +176,29 @@ docker run -d \
   upaas
 ```
 
+### Docker Compose
+
+```yaml
+services:
+  upaas:
+    build: .
+    restart: unless-stopped
+    ports:
+      - "8080:8080"
+    volumes:
+      - /var/run/docker.sock:/var/run/docker.sock
+      - ${HOST_DATA_DIR:-./data}:/var/lib/upaas
+    environment:
+      - UPAAS_HOST_DATA_DIR=${HOST_DATA_DIR:-./data}
+      # Optional: uncomment to enable debug logging
+      # - DEBUG=true
+      # Optional: Sentry error reporting
+      # - SENTRY_DSN=https://...
+      # Optional: Prometheus metrics auth
+      # - METRICS_USERNAME=prometheus
+      # - METRICS_PASSWORD=secret
+```
+
 **Important**: When running µPaaS inside a container, set `UPAAS_HOST_DATA_DIR` to the host path
 that maps to `UPAAS_DATA_DIR`. This is required for Docker bind mounts during builds to work correctly.