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/db/schema.ts

@@ -39,6 +39,15 @@ export const tipViews = sqliteTable('tip_views', {
   servedAt: text('served_at').notNull(),
 });
 
+export const pushSubscriptions = sqliteTable('push_subscriptions', {
+  id: text('id').primaryKey(),
+  userId: text('user_id').notNull().references(() => users.id),
+  endpoint: text('endpoint').notNull().unique(),
+  p256dh: text('p256dh').notNull(),
+  auth: text('auth').notNull(),
+  createdAt: text('created_at').notNull(),
+});
+
 export const sessions = sqliteTable('sessions', {
   id: text('id').primaryKey(),
   userId: text('user_id').notNull().references(() => users.id),