feat(observability): structured logs, W3C trace IDs, Sentry hooks (#18)

- TS: pino + pino-http; every HTTP request log includes traceId from
  W3C traceparent header (generated if absent); forwarded to ml/serving
  on all /score, /generate, /reward, and /api/ml proxy calls
- Python: structlog JSON; FastAPI middleware binds trace_id via
  contextvars so every log line within a request carries it
- Sentry: optional SENTRY_DSN init in both runtimes (no-op if unset)
- Replace all console.* calls across services/api with pino logger
- Update tests to spy on logger instead of console

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

services/api/package.json

@@ -16,6 +16,7 @@
   },
   "dependencies": {
     "@oo/shared-types": "workspace:*",
+    "@sentry/node": "^10.50.0",
     "better-sqlite3": "^11.8.1",
     "cookie-parser": "^1.4.7",
     "cors": "^2.8.5",
@@ -27,6 +28,8 @@
     "nats": "^2.29.3",
     "node-fetch": "^3.3.2",
     "openid-client": "^6.3.4",
+    "pino": "^10.3.1",
+    "pino-http": "^11.0.0",
     "web-push": "^3.6.7",
     "zod": "^3.24.1"
   },