refactor: remove warning-only code path for state root validation

- Remove conditional checks for settings.enforce_state_root_validation
- Always enforce state root validation (no warning-only path)
- Simplify error handling to always reject on mismatch
- Update genesis metadata validation to always enforce
- State root validation is now mandatory across all nodes

docs/apps/blockchain/blockchain-node.md

@@ -13,7 +13,8 @@ Production-ready blockchain node for AITBC with fixed supply and secure key mana
 - RESTful RPC API (`/rpc/*`)
 - Prometheus metrics (`/metrics`)
 - Health check endpoint (`/health`)
-- SQLite persistence with Alembic migrations
+- PostgreSQL mempool persistence (production nodes)
+- SQLite chain database with Alembic migrations
 - Multi-chain support (separate data directories per chain ID)
 
 ## Architecture

docs/apps/coordinator/coordinator-api.md

@@ -35,6 +35,14 @@ Set `VITE_DATA_MODE=live` and `VITE_COORDINATOR_API` in the explorer web app to
 
 Expects environment variables defined in `.env` (see `docs/bootstrap/coordinator_api.md`).
 
+### Database
+
+Production deployments use PostgreSQL for persistence. Configure via:
+- `DATABASE_ADAPTER=postgresql`
+- `DATABASE_URL=postgresql+psycopg://user:pass@localhost:5432/aitbc_coordinator`
+
+SQLite fallback is available for development or nodes without PostgreSQL.
+
 ### Signed receipts (optional)
 
 - Generate an Ed25519 key:

docs/apps/exchange/exchange.md

@@ -28,7 +28,7 @@ Cross-chain exchange and trading platform supporting multiple blockchain network
 
 ### Prerequisites
 - Python 3.13+
-- PostgreSQL database
+- PostgreSQL database (production default)
 - Redis for caching
 - Access to blockchain RPC endpoints