v2 restructure: Go client, Docker engine, release tooling

- Remove v1 Python CLI (src/kb_search/, tests/, root pyproject.toml, uv.lock, .venv)
- Add Go client with cross-platform build (client/)
- Add FastAPI engine with NVIDIA and multi-stage ROCm Dockerfiles (engine/)
- Add VERSION files for client and engine, wired into builds
- Add release.sh for automated build, tag, release, and Docker push
- Update README with build/release docs and ROCm migration note
- Clean up .gitignore for v2 project structure

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

.gitignore

@@ -1,8 +1 @@
-.venv/
-__pycache__/
-*.egg-info/
-*.pyc
-dist/
-build/
-.eggs/
 examples/