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/telemetry/worker-tracing.ts

@@ -0,0 +1,20 @@
+import "dotenv/config"; // Load env vars before checking OTEL_ENABLED
+import { isOtelEnabled } from "./index";
+import type { NodeSDK } from "@opentelemetry/sdk-node";
+
+let sdk: NodeSDK | null = null;
+
+if (isOtelEnabled) {
+  const { createNodeSDK } = require("./sdk-factory") as typeof import("./sdk-factory");
+  const { HttpInstrumentation } = require("@opentelemetry/instrumentation-http");
+  const { IORedisInstrumentation } = require("@opentelemetry/instrumentation-ioredis");
+
+  sdk = createNodeSDK({
+    serviceName: process.env.OTEL_SERVICE_NAME || "sase-worker",
+    instrumentations: [new HttpInstrumentation(), new IORedisInstrumentation()],
+  });
+} else {
+  console.log("[worker][otel] Telemetry disabled (OTEL_ENABLED !== 'true')");
+}
+
+export { sdk };