feat: establish sbom nexus extraction slice

Assistant: codex
Assistant-Model: gpt-5.6-sol
Assistant-Session: 01a028f0-a42f-7582-89a8-ebaad7343834

README.md

@@ -1,3 +1,32 @@
 # sbom-nexus
 
-A sbom management service
+SBOM Nexus is the dedicated software-bill-of-materials service for the Coulomb
+fleet. It captures dependency evidence from repositories, keeps immutable
+snapshots, evaluates licence risk and freshness, and provides a bounded catch-up
+queue for automation.
+
+The product direction is defined in [INTENT.md](INTENT.md). The first delivery
+contract is in [ProductRequirementsDocument.md](ProductRequirementsDocument.md).
+
+## Development
+
+```bash
+uv sync --dev
+uv run pytest
+uv run ruff check src tests
+uv run sbom-nexus serve --reload
+```
+
+The default API listens on `http://127.0.0.1:8010`. Its data location can be
+changed with `SBOM_NEXUS_DATABASE_PATH`.
+
+## Initial API surface
+
+- `GET /state/health`
+- `PUT /repositories/{repo_slug}`
+- `GET /sbom/catch-up?limit=3`
+- `POST /sbom/{repo_slug}/ingest`
+- State Hub-compatible `/sbom/` snapshot, entry, repository, and licence routes
+
+See [docs/state-hub-sbom-extraction-review.md](docs/state-hub-sbom-extraction-review.md)
+for the extraction inventory and cutover dispositions.