feat: v9.8.1 pre-built Docker images and GHCR release workflow

Setup.py now asks whether to pull pre-built images from GHCR
(recommended) or build from source. Pre-built mode skips the
15-minute compile step entirely.

- Add .github/workflows/release.yml (builds+pushes 4 images on tag)
- Add docker-compose.build.yml (source-build overlay)
- Switch docker-compose.prod.yml from build: to image: refs
- Add --build-mode CLI arg and wizard step to setup.py
- Bump version to 9.8.1 across all files
- Document TOD_VERSION env var in CONFIGURATION.md

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

VERSION

@@ -1 +1 @@
-9.8.0
+9.8.1