Wire up remaining TODO stubs: P3 test notifications, P2 drift notification trigger

- P3: test notification endpoint now instantiates real Slack/Email/Webhook notifiers
- P2: drift processor triggers notification service when drift_score > 0 (non-fatal on failure)

products/03-alert-intelligence/src/api/notifications.ts

@@ -50,8 +50,35 @@ export function registerNotificationRoutes(app: FastifyInstance) {
     const { channel } = req.params as { channel: string };
     const tenantId = (req as any).tenantId;
 
-    // TODO: Send test notification via the configured channel
-    logger.info({ tenantId, channel }, 'Test notification sent');
-    return { status: 'sent', channel };
+    const configResult = await withTenant(tenantId, async (client) => {
+      return client.query('SELECT * FROM notification_configs WHERE channel = $1', [channel]);
+    });
+
+    const cfg = configResult.rows[0];
+    if (!cfg) return reply.status(404).send({ error: `No ${channel} config found` });
+
+    const { SlackNotifier, EmailNotifier, WebhookNotifier } = await import('../notifications/dispatcher.js');
+    const testIncident = {
+      incidentId: 'test-000',
+      title: '[TEST] dd0c/alert notification test',
+      severity: 'info',
+      service: 'test-service',
+      alertCount: 1,
+      firstAlertAt: new Date(),
+      fingerprint: 'test',
+      dashboardUrl: `https://alert.dd0c.dev/incidents/test-000`,
+    };
+
+    let sent = false;
+    if (channel === 'slack' && cfg.config?.slack_webhook_url) {
+      sent = await new SlackNotifier(cfg.config.slack_webhook_url).send(testIncident);
+    } else if (channel === 'email' && cfg.config?.email_to) {
+      sent = await new EmailNotifier(process.env.RESEND_API_KEY ?? '', 'alerts@dd0c.dev', cfg.config.email_to).send(testIncident);
+    } else if (channel === 'webhook' && cfg.config?.webhook_url) {
+      sent = await new WebhookNotifier(cfg.config.webhook_url).send(testIncident);
+    }
+
+    logger.info({ tenantId, channel, sent }, 'Test notification sent');
+    return { status: sent ? 'sent' : 'failed', channel };
   });
 }