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.

services/sanctions/chaos.py

@@ -0,0 +1,37 @@
+"""slow_sanctions and sanctions_errors -- phase-0-base-project-spec.md §7.
+
+Both flags belong to `sanctions`, the fake third-party watchlist vendor.
+"""
+import math
+import random
+
+from common.chaos_flags import is_enabled
+
+_MEDIAN_SECONDS = 0.04
+_P99_SECONDS = 1.8
+_MU = math.log(_MEDIAN_SECONDS)
+_Z99 = 2.326347874
+_SIGMA = (math.log(_P99_SECONDS) - _MU) / _Z99
+_TIMEOUT_TRIGGER_PROBABILITY = 0.015
+_TIMEOUT_TRIGGER_SECONDS = 5.0
+_ERROR_PROBABILITY = 0.03
+
+
+async def slow_sanctions_enabled() -> bool:
+    return await is_enabled("slow_sanctions")
+
+
+async def sanctions_errors_enabled() -> bool:
+    return await is_enabled("sanctions_errors")
+
+
+def sample_delay_seconds() -> float:
+    """Log-normal delay: median ~40ms, p99 ~1.8s. 1.5% of calls sleep 5s,
+    which exceeds the caller's 3s downstream timeout and surfaces as one."""
+    if random.random() < _TIMEOUT_TRIGGER_PROBABILITY:
+        return _TIMEOUT_TRIGGER_SECONDS
+    return random.lognormvariate(_MU, _SIGMA)
+
+
+def should_error() -> bool:
+    return random.random() < _ERROR_PROBABILITY