feat(notifications): add unified multi-channel notification system

Introduces a fully featured notification system with three delivery
channels (in-app, email, webhook), normalized per-user/per-event/
per-channel preferences, admin-scoped notifications, scheduled trip
reminders and version update alerts.

- New notificationService.send() as the single orchestration entry point
- In-app notifications with simple/boolean/navigate types and WebSocket push
- Per-user preference matrix with normalized notification_channel_preferences table
- Admin notification preferences stored globally in app_settings
- Migration 69 normalizes legacy notification_preferences table
- Scheduler hooks for daily trip reminders and version checks
- DevNotificationsPanel for testing in dev mode
- All new tests passing, covering dispatch, preferences, migration, boolean
  responses, resilience, and full API integration (NSVC, NPREF, INOTIF,
  MIGR, VNOTIF, NROUTE series)
 - Previous tests passing

server/src/db/migrations.ts

@@ -550,6 +550,58 @@ function runMigrations(db: Database.Database): void {
         );
       `);
     },
+    // Migration 69: Normalized per-user per-channel notification preferences
+    () => {
+      db.exec(`
+        CREATE TABLE IF NOT EXISTS notification_channel_preferences (
+          user_id INTEGER NOT NULL REFERENCES users(id) ON DELETE CASCADE,
+          event_type TEXT NOT NULL,
+          channel TEXT NOT NULL,
+          enabled INTEGER NOT NULL DEFAULT 1,
+          PRIMARY KEY (user_id, event_type, channel)
+        );
+        CREATE INDEX IF NOT EXISTS idx_ncp_user ON notification_channel_preferences(user_id);
+      `);
+
+      // Migrate data from old notification_preferences table
+      const oldPrefs = db.prepare('SELECT * FROM notification_preferences').all() as Array<Record<string, number>>;
+      const eventCols: Record<string, string> = {
+        trip_invite: 'notify_trip_invite',
+        booking_change: 'notify_booking_change',
+        trip_reminder: 'notify_trip_reminder',
+        vacay_invite: 'notify_vacay_invite',
+        photos_shared: 'notify_photos_shared',
+        collab_message: 'notify_collab_message',
+        packing_tagged: 'notify_packing_tagged',
+      };
+      const insert = db.prepare(
+        'INSERT OR IGNORE INTO notification_channel_preferences (user_id, event_type, channel, enabled) VALUES (?, ?, ?, ?)'
+      );
+      const insertMany = db.transaction((rows: Array<[number, string, string, number]>) => {
+        for (const [userId, eventType, channel, enabled] of rows) {
+          insert.run(userId, eventType, channel, enabled);
+        }
+      });
+
+      for (const row of oldPrefs) {
+        const userId = row.user_id as number;
+        const webhookEnabled = (row.notify_webhook as number) ?? 0;
+        const rows: Array<[number, string, string, number]> = [];
+        for (const [eventType, col] of Object.entries(eventCols)) {
+          const emailEnabled = (row[col] as number) ?? 1;
+          // Only insert if disabled (no row = enabled is our default)
+          if (!emailEnabled) rows.push([userId, eventType, 'email', 0]);
+          if (!webhookEnabled) rows.push([userId, eventType, 'webhook', 0]);
+        }
+        if (rows.length > 0) insertMany(rows);
+      }
+
+      // Copy existing single-channel setting to new plural key
+      db.exec(`
+        INSERT OR IGNORE INTO app_settings (key, value)
+          SELECT 'notification_channels', value FROM app_settings WHERE key = 'notification_channel';
+      `);
+    },
   ];
 
   if (currentVersion < migrations.length) {

server/src/db/schema.ts

@@ -418,6 +418,15 @@ function createTables(db: Database.Database): void {
     );
     CREATE INDEX IF NOT EXISTS idx_notifications_recipient ON notifications(recipient_id, is_read, created_at DESC);
     CREATE INDEX IF NOT EXISTS idx_notifications_recipient_created ON notifications(recipient_id, created_at DESC);
+
+    CREATE TABLE IF NOT EXISTS notification_channel_preferences (
+      user_id INTEGER NOT NULL REFERENCES users(id) ON DELETE CASCADE,
+      event_type TEXT NOT NULL,
+      channel TEXT NOT NULL,
+      enabled INTEGER NOT NULL DEFAULT 1,
+      PRIMARY KEY (user_id, event_type, channel)
+    );
+    CREATE INDEX IF NOT EXISTS idx_ncp_user ON notification_channel_preferences(user_id);
   `);
 }