* fix: add procps to Docker image and smoke test to release workflow
The Docker image was failing to start because pg0 uses `kill -0 <pid>`
to check if PostgreSQL is running, but the python:3.11-slim base image
doesn't include the `kill` command. Adding procps provides it.
This has been broken since release 0.1.6 when the fallback URI code was
removed to support dynamic ports. Without the kill command, pg0 couldn't
detect process status and returned None for the database URI.
Also adds smoke testing to the release workflow:
- Build image locally (single platform) and test before pushing
- Run container and wait for /health endpoint (up to 120s)
- Only push multi-platform release images if smoke test passes
- Each image (api-only, cp-only, standalone) tested independently
This prevents releasing broken Docker images to GHCR.
* refactor: extract smoke test into reusable script
Add scripts/docker-smoke-test.sh that can be run locally or in CI:
- Takes image name and optional target (cp-only vs api)
- Handles LLM credentials for API/standalone images
- Configurable timeout via SMOKE_TEST_TIMEOUT env var
- Colored output and clear error messages
- Proper cleanup on exit
Update release workflow to use the script instead of inline bash.
