feat: M1 — LinUCB bandit, RemotePolicy, Web Push, event bus

ML serving:
- LinUCB contextual bandit (disjoint, d=5 features: hour_sin/cos, is_overdue, task_age, priority)
- /score endpoint replaces stub random; /reward endpoint for online learning
- Per-user model state persisted to disk as JSON (survives restarts)
- venv at ml/serving/.venv; start with pnpm dev from ml/serving

Recommender:
- Todoist fetch now extracts features (is_overdue, task_age_days, priority)
- RemotePolicy calls ml/serving with 3s timeout; falls back to RandomPolicy
- Reward sent to /reward on feedback (done=+1, snooze=0, dismiss=-1)

Web Push:
- VAPID keys in config; push_subscriptions table in DB
- POST/DELETE /api/push/subscribe; GET /api/push/vapid-public-key
- Service worker (public/sw.js): push → showNotification, notificationclick → focus/open
- "notify me" button on tip page; registers SW + subscribes on permission grant

Event bus:
- services/api/src/events/bus.ts: typed EventEmitter wrapper
- Subjects: signals.tip.served, signals.tip.feedback, signals.task.synced
- Same publish/subscribe API NATS JetStream will implement — swap is mechanical

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

services/api/src/events/bus.ts

@@ -0,0 +1,52 @@
+/**
+ * EventBus — in-process today, NATS JetStream tomorrow.
+ *
+ * To swap to NATS: replace the EventEmitter body with a NATS JetStream
+ * publish call. Subjects and payload shapes are the durable contract.
+ *
+ * Subjects follow the pattern: <domain>.<entity>.<verb>
+ *   signals.tip.served      — a tip was returned to the client
+ *   signals.tip.feedback    — user reacted (done / dismiss / snooze)
+ *   signals.task.synced     — Todoist task list refreshed for a user
+ */
+
+import { EventEmitter } from 'events';
+
+export type TipServedEvent = {
+  userId: string;
+  tipId: string;
+  policy: string;
+  servedAt: string;
+};
+
+export type TipFeedbackEvent = {
+  userId: string;
+  tipId: string;
+  action: 'done' | 'dismiss' | 'snooze';
+  reward: number;
+  createdAt: string;
+};
+
+export type TaskSyncedEvent = {
+  userId: string;
+  count: number;
+  syncedAt: string;
+};
+
+type EventMap = {
+  'signals.tip.served': TipServedEvent;
+  'signals.tip.feedback': TipFeedbackEvent;
+  'signals.task.synced': TaskSyncedEvent;
+};
+
+class Bus extends EventEmitter {
+  publish<K extends keyof EventMap>(subject: K, payload: EventMap[K]): void {
+    this.emit(subject, payload);
+  }
+
+  subscribe<K extends keyof EventMap>(subject: K, handler: (payload: EventMap[K]) => void): void {
+    this.on(subject, handler);
+  }
+}
+
+export const bus = new Bus();