feat: add OpenTelemetry observability, Faro frontend monitoring, remove legacy Next.js app

- Add OpenTelemetry SDK with tracing, metrics, and OTLP export for API and worker
- Integrate Grafana Faro for frontend real-user monitoring
- Instrument health checks, database, Bull queues, and HTTP exception filter
- Add Grafana dashboard JSON for service overview
- Remove deprecated apps/web-nj (Next.js) — fully replaced by Vite+React frontend
- Update nginx config with OTEL collector proxy
- Minor UI fixes in schema viewer, category components, and subscription flow

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

apps/api/src/main.ts

@@ -1,3 +1,5 @@
+import "./telemetry/tracing"; // MUST be first — instruments modules before they load
+
 import { NestFactory } from "@nestjs/core";
 import { ConfigService } from "@nestjs/config";
 import helmet from "helmet";
@@ -21,7 +23,7 @@ async function bootstrap() {
     origin: corsOrigins,
     credentials: true,
     methods: ["GET", "POST", "PUT", "PATCH", "DELETE", "OPTIONS"],
-    allowedHeaders: ["Content-Type", "Authorization", "Cookie"],
+    allowedHeaders: ["Content-Type", "Authorization", "Cookie", "traceparent", "tracestate"],
     exposedHeaders: ["set-cookie"],
     maxAge: 86400,
   });