chore: initialize monorepo with project scaffolding, configs, and CI setup

apps/coordinator-api/README.md

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+# Coordinator API
+
+## Purpose & Scope
+
+FastAPI service that accepts client compute jobs, matches miners, and tracks job lifecycle for the AITBC network.
+
+## Development Setup
+
+1. Create a virtual environment in `apps/coordinator-api/.venv`.
+2. Install dependencies listed in `pyproject.toml` once added.
+3. Run the FastAPI app via `uvicorn app.main:app --reload`.
+
+## Configuration
+
+Expects environment variables defined in `.env` (see `docs/bootstrap/coordinator_api.md`).
+
+### Signed receipts (optional)
+
+- Generate an Ed25519 key:
+  ```bash
+  python - <<'PY'
+  from nacl.signing import SigningKey
+  sk = SigningKey.generate()
+  print(sk.encode().hex())
+  PY
+  ```
+- Set `RECEIPT_SIGNING_KEY_HEX` in the `.env` file to the printed hex string to enable signed receipts returned by `/v1/miners/{job_id}/result` and retrievable via `/v1/jobs/{job_id}/receipt`.
+- Receipt history is available at `/v1/jobs/{job_id}/receipts` (requires client API key) and returns all stored signed payloads.
+- To enable coordinator attestations, set `RECEIPT_ATTESTATION_KEY_HEX` to a separate Ed25519 private key; responses include an `attestations` array alongside the miner signature.
+- Clients can verify `signature` objects using the `aitbc_crypto` package (see `protocols/receipts/spec.md`).
+
+## Systemd
+
+Service name: `aitbc-coordinator-api` (to be defined under `configs/systemd/`).