feat(monitoring): add Prometheus metrics endpoint and Grafana dashboards

Add observability stack with @willsoto/nestjs-prometheus for /metrics endpoint,
Prometheus scraping config, and 4 auto-provisioned Grafana dashboards
(API overview, database, search, business metrics).

Co-Authored-By: Paperclip <noreply@paperclip.ing>

apps/api/src/app.module.ts

@@ -6,6 +6,7 @@ import { NotificationsModule } from '@modules/notifications';
 import { PaymentsModule } from '@modules/payments';
 import { SubscriptionsModule } from '@modules/subscriptions';
 import { AdminModule } from '@modules/admin';
+import { MetricsModule } from '@modules/metrics';
 import { Module } from '@nestjs/common';
 import { APP_GUARD } from '@nestjs/core';
 import { CqrsModule } from '@nestjs/cqrs';
@@ -24,6 +25,7 @@ import { AppController } from './app.controller';
     PaymentsModule,
     SubscriptionsModule,
     AdminModule,
+    MetricsModule,
 
     // ── Rate Limiting ──
     // Default: 60 requests per 60 seconds per IP