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>

ml/serving/nats_consumer.py

@@ -17,15 +17,15 @@ Config (env vars):
 from __future__ import annotations
 
 import json
-import logging
 import os
 import time
 from pathlib import Path
 from typing import Optional
 
+import structlog
 from schemas import TaskSyncedPayload, TipFeedbackPayload
 
-logger = logging.getLogger(__name__)
+log = structlog.get_logger(__name__)
 
 NATS_URL = os.getenv("NATS_URL", "")
 NATS_DURABLE_PREFIX = os.getenv("NATS_DURABLE_PREFIX", "feature-pipeline")
@@ -56,15 +56,12 @@ async def _handle(subject: str, payload: dict, state_dir: Path) -> None:
             "last_sync_ts": msg.syncedAt,
             "task_count": msg.count,
         }))
-        logger.info("[nats] task_synced user=%s count=%s", msg.userId, msg.count)
+        log.info("nats: task_synced", user_id=msg.userId, count=msg.count)
     elif subject == "signals.tip.feedback":
         msg = TipFeedbackPayload.model_validate(payload)
-        logger.info(
-            "[nats] tip_feedback user=%s tip=%s action=%s reward=%s",
-            msg.userId, msg.tipId, msg.action, msg.reward,
-        )
+        log.info("nats: tip_feedback", user_id=msg.userId, tip_id=msg.tipId, action=msg.action, reward=msg.reward)
     else:
-        logger.debug("[nats] unhandled subject=%s", subject)
+        log.debug("nats: unhandled subject", subject=subject)
 
 
 # ── Consumer factory ───────────────────────────────────────────────────────
@@ -80,7 +77,7 @@ def _make_handler(key: str, state_dir: Path):
             consumer_health[key]["processed"] += 1
         except Exception as exc:
             consumer_health[key]["errors"] += 1
-            logger.warning("[nats] processing error key=%s subject=%s: %s", key, msg.subject, exc)
+            log.warning("nats: processing error", key=key, subject=msg.subject, exc=str(exc))
             await msg.nak()
     return handler
 
@@ -91,7 +88,7 @@ async def start(state_dir: Path) -> None:
     """Connect to NATS and register durable push consumers. No-op if NATS_URL is unset."""
     global _nc
     if not NATS_URL:
-        logger.info("[nats] NATS_URL unset — JetStream consumers disabled")
+        log.info("nats: NATS_URL unset — JetStream consumers disabled")
         return
 
     try:
@@ -105,9 +102,9 @@ async def start(state_dir: Path) -> None:
             max_reconnect_attempts=-1,
         )
         js = _nc.jetstream()
-        logger.info("[nats] connected to %s", NATS_URL)
+        log.info("nats: connected", url=NATS_URL)
     except Exception as exc:
-        logger.warning("[nats] connection failed: %s — consumers disabled", exc)
+        log.warning("nats: connection failed — consumers disabled", exc=str(exc))
         _nc = None
         return
 
@@ -126,9 +123,9 @@ async def start(state_dir: Path) -> None:
                 config=config,
             )
             _subs.append(sub)
-            logger.info("[nats] subscribed subject=%s durable=%s", subject, durable)
+            log.info("nats: subscribed", subject=subject, durable=durable)
         except Exception as exc:
-            logger.warning("[nats] subscribe failed key=%s: %s", key, exc)
+            log.warning("nats: subscribe failed", key=key, exc=str(exc))
 
 
 async def stop() -> None:
@@ -146,4 +143,4 @@ async def stop() -> None:
         except Exception:
             pass
         _nc = None
-        logger.info("[nats] disconnected")
+        log.info("nats: disconnected")