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

apps/blockchain-node/README.md

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+# Blockchain Node
+
+## Purpose & Scope
+
+Minimal asset-backed blockchain node that validates compute receipts and mints AIT tokens as described in `docs/bootstrap/blockchain_node.md`.
+
+## Status
+
+Scaffolded. Implementation pending per staged roadmap.
+
+## Devnet Tooling
+
+- `scripts/make_genesis.py` — Generate a deterministic devnet genesis file (`data/devnet/genesis.json`).
+- `scripts/keygen.py` — Produce throwaway devnet keypairs (printed or written to disk).
+- `scripts/devnet_up.sh` — Launch the blockchain node and RPC API with a freshly generated genesis file.
+
+### Quickstart
+
+```bash
+cd apps/blockchain-node
+python scripts/make_genesis.py --force
+bash scripts/devnet_up.sh
+```
+
+The script sets `PYTHONPATH=src` and starts the proposer loop plus the FastAPI app (via `uvicorn`). Press `Ctrl+C` to stop the devnet.