feat: M1 admin console — all 10 remaining pages + signal/quality/ops infrastructure

Admin console (issues #63–72):
- Event stream viewer: live-tail ring buffer (500 events) with subject/user filters
- Feature store browser: per-user feature vector history from ml/serving
- Model registry panel: MLflow embed at /admin/models
- Experiment dashboard: LinUCB per-user stats (pulls, reward, θ) + bandit reset
- Recommendation log: per-tip explainability (policy, score, features, latency)
- Reward analytics: daily reaction breakdown + per-policy compare
- Data quality widget: missing-feature rate, stale-token rate, daily completeness
- Ops actions: replay-signal, policy enable/disable; user actions link to Users page
- SQL runner: read-only SELECT runner with saved queries
- Health rollup: fan-out to api/ml/sqlite/event-bus with auto-refresh

Backend:
- tip_scores table: logs features+policy+score+latency at every scoring call (#67)
- saved_queries table: per-admin saved SQL (#71)
- Event bus: 500-event ring buffer + tail() API (#63)
- Admin routes: /events, /tips, /reward-analytics, /data-quality, /health,
  /policies, /replay-signal, /sql, /saved-queries endpoints
- /api/ml/* admin-gated proxy to ml/serving (#64, #66)
- Shadow-policy registry in recommender (#56)

ML serving:
- /reset/{user_id}: clear bandit state + feature history (#66)
- /stats/{user_id}: pulls, cumulative reward, estimated mean, θ (#66)
- /features/{user_id}: last 100 feature vectors logged at scoring time (#64)
- Meta (pulls, rewards) persisted alongside A/b matrices

Web:
- Tip action sheet adds Helpful / Not helpful buttons (#62)
- TipFeedback type extended with helpful/not_helpful actions
- Rewards mapped: helpful=+0.5, not_helpful=−0.5

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

services/api/src/events/bus.ts

@@ -22,7 +22,7 @@ export type TipServedEvent = {
 export type TipFeedbackEvent = {
   userId: string;
   tipId: string;
-  action: 'done' | 'dismiss' | 'snooze';
+  action: 'done' | 'dismiss' | 'snooze' | 'helpful' | 'not_helpful';
   reward: number;
   createdAt: string;
 };
@@ -39,14 +39,56 @@ type EventMap = {
   'signals.task.synced': TaskSyncedEvent;
 };
 
+export type StoredEvent = {
+  id: number;
+  subject: string;
+  payload: unknown;
+  ts: string;
+};
+
+const RING_SIZE = 500;
+
 class Bus extends EventEmitter {
+  private ring: StoredEvent[] = [];
+  private seq = 0;
+
   publish<K extends keyof EventMap>(subject: K, payload: EventMap[K]): void {
+    const entry: StoredEvent = {
+      id: ++this.seq,
+      subject,
+      payload,
+      ts: new Date().toISOString(),
+    };
+    if (this.ring.length >= RING_SIZE) this.ring.shift();
+    this.ring.push(entry);
     this.emit(subject, payload);
   }
 
   subscribe<K extends keyof EventMap>(subject: K, handler: (payload: EventMap[K]) => void): void {
     this.on(subject, handler);
   }
+
+  /**
+   * Return recent events from the ring buffer.
+   * @param subject  optional filter (prefix match, e.g. "signals.tip")
+   * @param userId   optional user ID filter
+   * @param limit    max events to return (default 100)
+   * @param since    only events with id > since
+   */
+  tail(opts: { subject?: string; userId?: string; limit?: number; since?: number } = {}): StoredEvent[] {
+    const { subject, userId, limit = 100, since = 0 } = opts;
+    let results = this.ring.filter((e) => {
+      if (e.id <= since) return false;
+      if (subject && !e.subject.startsWith(subject)) return false;
+      if (userId) {
+        const p = e.payload as Record<string, unknown>;
+        if (p.userId !== userId) return false;
+      }
+      return true;
+    });
+    if (results.length > limit) results = results.slice(results.length - limit);
+    return results;
+  }
 }
 
 export const bus = new Bus();