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/src/signals/scheduler.ts

@@ -13,6 +13,7 @@ import { db } from '../db/index.js';
 import { integrationTokens } from '../db/schema.js';
 import { eq } from 'drizzle-orm';
 import { todoistSource } from './todoist.js';
+import { logger } from '../logger.js';
 
 const DEFAULT_INTERVAL_MS = 15 * 60 * 1000;
 
@@ -25,7 +26,7 @@ export function startTodoistSyncScheduler(intervalMs = DEFAULT_INTERVAL_MS): Nod
         .from(integrationTokens)
         .where(eq(integrationTokens.tokenStatus, 'active'));
     } catch (err: any) {
-      console.error(`[scheduler] failed to query users: ${err.message}`);
+      logger.error({ err }, 'scheduler: failed to query users');
       return;
     }
 
@@ -39,10 +40,10 @@ export function startTodoistSyncScheduler(intervalMs = DEFAULT_INTERVAL_MS): Nod
     let failed = 0;
     for (const r of results) {
       if (r.status === 'fulfilled') ok++;
-      else { failed++; console.error(`[scheduler] sync error:`, r.reason); }
+      else { failed++; logger.error({ err: r.reason }, 'scheduler: sync error'); }
     }
 
-    console.log(`[scheduler] todoist sync: ${ok} ok, ${failed} failed (${users.length} users)`);
+    logger.info({ ok, failed, total: users.length }, 'scheduler: todoist sync');
   }
 
   // Run once shortly after startup, then on interval