feat(infra): add OTel auto-instrumentations across all services

NestJS 6 services use getNodeAutoInstrumentations().

Python 2 services use FastAPIInstrumentor. Go 2 services use otelgin.

services/teacher-bff/src/main.ts

@@ -1,11 +1,13 @@
-import 'reflect-metadata';
-import { NestFactory } from '@nestjs/core';
-import { AppModule } from './app.module.js';
-import { env } from './config/env.js';
+import "reflect-metadata";
+import { NestFactory } from "@nestjs/core";
+import { AppModule } from "./app.module.js";
+import { env } from "./config/env.js";
+import { initTracer, shutdownTracer } from "./shared/observability/tracer.js";
 
 async function bootstrap(): Promise<void> {
+  initTracer();
   const app = await NestFactory.create(AppModule, {
-    logger: ['log', 'error', 'warn'],
+    logger: ["log", "error", "warn"],
   });
 
   app.enableShutdownHooks();
@@ -13,12 +15,13 @@ async function bootstrap(): Promise<void> {
   await app.listen(env.PORT);
   console.log(`Teacher BFF started on port ${env.PORT}`);
 
-  process.on('SIGTERM', async () => {
+  process.on("SIGTERM", async () => {
     await app.close();
+    await shutdownTracer();
   });
 }
 
 bootstrap().catch((err: unknown) => {
-  console.error('Failed to start Teacher BFF', err);
+  console.error("Failed to start Teacher BFF", err);
   process.exit(1);
 });