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>

apps/web/src/lib/api.ts

@@ -62,3 +62,22 @@ export async function deleteAccount() {
 export async function logout() {
   return apiFetch<{ ok: boolean }>('/auth/logout', { method: 'POST' });
 }
+
+export async function getVapidPublicKey(): Promise<string> {
+  const { key } = await apiFetch<{ key: string }>('/push/vapid-public-key');
+  return key;
+}
+
+export async function subscribePush(subscription: PushSubscriptionJSON) {
+  return apiFetch<{ ok: boolean }>('/push/subscribe', {
+    method: 'POST',
+    body: JSON.stringify(subscription),
+  });
+}
+
+export async function unsubscribePush(endpoint: string) {
+  return apiFetch<{ ok: boolean }>('/push/subscribe', {
+    method: 'DELETE',
+    body: JSON.stringify({ endpoint }),
+  });
+}