feat(09-01): add owner_user_id to notification_channels + event-key and subscription tables

- migrations/085: ALTER TABLE notification_channels ADD COLUMN owner_user_id TEXT REFERENCES user(id) ON DELETE CASCADE
- migrations/085: partial unique index notification_channels_owner_user_id_channel_type_uniq WHERE owner_user_id IS NOT NULL (UPSERT race defense)
- migrations/086: CREATE TABLE notify_event_keys (key PK, display_label, description, sort_order, is_active) with seed row
- migrations/086: CREATE TABLE user_event_subscriptions composite PK (user_id, event_key, channel_type) opt-out model
- lib/types/pipeline.ts: NotificationChannel gains owner_user_id: string | null
- lib/types/pipeline.ts: exports NotifyEventKey and UserEventSubscription interfaces

lib/types/pipeline.ts

@@ -44,6 +44,7 @@ export interface NotificationChannel {
   channel_type: ChannelType;
   config: Record<string, any>;
   is_active: boolean;
+  owner_user_id: string | null;
   created_at: Date;
   updated_at: Date;
 }
@@ -169,3 +170,25 @@ export interface NotificationChannelInput {
   config: Record<string, any>;
   is_active?: boolean;
 }
+
+// ============================================================================
+// Phase 9 — Event taxonomy + user subscriptions
+// ============================================================================
+
+export interface NotifyEventKey {
+  key: string;
+  display_label: string;
+  description: string | null;
+  sort_order: number;
+  is_active: boolean;
+  created_at: Date;
+  updated_at: Date;
+}
+
+export interface UserEventSubscription {
+  user_id: string;
+  event_key: string;
+  channel_type: ChannelType;
+  enabled: boolean;
+  updated_at: Date;
+}