feat(metrics): Prometheus queue metrics for BullMQ (RFC-004 Phase 3 WS3a)

Adds a 5 s polling collector that publishes BullMQ queue depth as the
goodgo_queue_depth gauge (labels: queue, state) and a
goodgo_queue_job_outcomes_total counter for processor hooks. The collector
fails-soft on Redis errors so a queue blip cannot crash the app.

- New constants: QUEUE_DEPTH_GAUGE, QUEUE_JOB_OUTCOMES_TOTAL,
  QUEUE_METRICS_QUEUE_NAMES (extend as Phase 2 adds queues)
- New QueueMetricsCollector with injectable timer/clock for tests
- MetricsModule.withQueueMetrics() dynamic module wires queue tokens via
  getQueueToken + factory provider; re-imports BullModule.registerQueue so
  ordering between MetricsModule and feature modules does not matter
- AppModule mounts MetricsModule.withQueueMetrics() alongside MetricsModule
- 4 unit tests cover sample → gauge mapping, Redis-down fail-soft,
  recordJobOutcome, and timer init/destroy

Bull Board UI mount split into WS3b (needs @bull-board/* deps).

Refs: GOO-175

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

apps/api/src/modules/metrics/metrics.module.ts

@@ -1,10 +1,24 @@
-import { Module } from '@nestjs/common';
+import { BullModule, getQueueToken } from '@nestjs/bullmq';
+import { Module, type DynamicModule } from '@nestjs/common';
 import {
   makeCounterProvider,
   makeHistogramProvider,
   makeGaugeProvider,
 } from '@willsoto/nestjs-prometheus';
+import type { Queue } from 'bullmq';
 import { MetricsService } from './infrastructure/metrics.service';
+import {
+  QueueMetricsCollector,
+  QUEUE_METRICS_COLLECTOR_OPTIONS,
+  QUEUE_METRICS_COLLECTOR_QUEUES,
+  type QueueLike,
+  type QueueMetricsCollectorOptions,
+} from './infrastructure/queue-metrics.collector';
+import {
+  QUEUE_DEPTH_GAUGE,
+  QUEUE_JOB_OUTCOMES_TOTAL,
+  QUEUE_METRICS_QUEUE_NAMES,
+} from './infrastructure/queue-metrics.constants';
 import {
   GOODGO_API_REQUEST_DURATION,
   GOODGO_LISTINGS_CREATED_TOTAL,
@@ -141,4 +155,48 @@ import { HttpMetricsInterceptor } from './presentation/interceptors/http-metrics
   controllers: [WebVitalsController],
   exports: [MetricsService, HttpMetricsInterceptor],
 })
-export class MetricsModule {}
+export class MetricsModule {
+  /**
+   * Register the queue-metrics collector with a fixed list of BullMQ queue
+   * names. Each name must already be registered via BullModule.registerQueue
+   * somewhere in the app (root or feature module).
+   *
+   * RFC-004 Phase 3 — workstream 3a.
+   */
+  static withQueueMetrics(
+    queueNames: readonly string[] = QUEUE_METRICS_QUEUE_NAMES,
+    options: QueueMetricsCollectorOptions = {},
+  ): DynamicModule {
+    const queueTokens = queueNames.map((name) => getQueueToken(name));
+    return {
+      module: MetricsModule,
+      imports: [
+        // Re-register each queue here so the collector can resolve them via
+        // BullMQ's standard token even if MetricsModule is imported before
+        // the feature module that owns the queue. BullMQ deduplicates the
+        // queue instance under the hood.
+        ...queueNames.map((name) => BullModule.registerQueue({ name })),
+      ],
+      providers: [
+        makeGaugeProvider({
+          name: QUEUE_DEPTH_GAUGE,
+          help: 'BullMQ queue depth by state (waiting, active, completed, failed, delayed)',
+          labelNames: ['queue', 'state'],
+        }),
+        makeCounterProvider({
+          name: QUEUE_JOB_OUTCOMES_TOTAL,
+          help: 'BullMQ job outcomes (completed, failed) by queue',
+          labelNames: ['queue', 'outcome'],
+        }),
+        {
+          provide: QUEUE_METRICS_COLLECTOR_QUEUES,
+          inject: queueTokens,
+          useFactory: (...queues: Queue[]): QueueLike[] => queues,
+        },
+        { provide: QUEUE_METRICS_COLLECTOR_OPTIONS, useValue: options },
+        QueueMetricsCollector,
+      ],
+      exports: [QueueMetricsCollector],
+    };
+  }
+}