Implement Phase 0b base project against the frozen test contract

All seven services (gateway, ledger, fraud, sanctions, insights, notifier,
audit), db/schema.sql plus optional_indexes.sql, scripts/seed.py and
smoke.py, the gateway-served frontend, and docker-compose.yml. Plain-text
stdlib logging and a weak manual X-Request-Id only -- no observability yet,
by design, per test_no_observability.py. Implements all 13 named chaos-flag
pathologies from docs/PATHOLOGIES.md behind Redis-backed runtime flags.

make smoke and make test-contract pass; make test-baseline and
make test-pathology pass except for a handful of load-sensitive tests
documented in tests/README.md rather than papered over.

.env.example

@@ -0,0 +1,14 @@
+# Copy to .env if you want to override defaults for a local, non-Compose run.
+# Inside Compose, these are set directly in docker-compose.yml per service.
+
+POSTGRES_DSN=postgresql+asyncpg://ledgerline:ledgerline@localhost:5432/ledgerline
+REDIS_URL=redis://localhost:6379/0
+
+GATEWAY_URL=http://localhost:8000
+LEDGER_URL=http://localhost:8001
+FRAUD_URL=http://localhost:8002
+SANCTIONS_URL=http://localhost:8003
+INSIGHTS_URL=http://localhost:8004
+NOTIFIER_URL=http://localhost:8005
+
+SEED=42