fix(infra): resolve NestJS dist build and Prometheus target issues

NestJS: disable incremental in 6 services tsconfig.json to fix dist
not emitted when nest-cli deleteOutDir conflicts with tsc tsbuildinfo.
classes/iam: import HealthModule in AppModule to fix /healthz 404.
classes: rewrite HealthController to Drizzle getDb from TypeORM DI.
teacher-bff: add /metrics endpoint for Prometheus scraping.
infra: add node/mysql/redis exporters to observability profile.
mysql-exporter v0.15.1 uses command-line flags not DATA_SOURCE_NAME.
prometheus: enable web.enable-lifecycle for hot reload.

services/classes/src/shared/health/health.controller.ts

@@ -1,7 +1,8 @@
-import { Controller, Get, HttpException, HttpStatus } from '@nestjs/common';
-import { DataSource } from 'typeorm';
+import { Controller, Get, HttpException, HttpStatus } from "@nestjs/common";
+import { sql } from "drizzle-orm";
+import { getDb } from "../../config/database.js";
 
-const SERVICE_NAME = 'classes';
+const SERVICE_NAME = "classes";
 
 /**
  * 健康检查端点。
@@ -14,33 +15,37 @@ const SERVICE_NAME = 'classes';
  */
 @Controller()
 export class HealthController {
-  constructor(private readonly dataSource: DataSource) {}
-
-  @Get('healthz')
+  @Get("healthz")
   liveness(): { status: string; service: string; timestamp: string } {
     return {
-      status: 'ok',
+      status: "ok",
       service: SERVICE_NAME,
       timestamp: new Date().toISOString(),
     };
   }
 
-  @Get('readyz')
-  async readiness(): Promise<{ status: string; service: string; timestamp: string }> {
+  @Get("readyz")
+  async readiness(): Promise<{
+    status: string;
+    service: string;
+    timestamp: string;
+  }> {
     try {
-      await this.dataSource.query('SELECT 1');
+      const db = getDb();
+      await db.execute(sql`SELECT 1`);
       return {
-        status: 'ok',
+        status: "ok",
         service: SERVICE_NAME,
         timestamp: new Date().toISOString(),
       };
     } catch (error) {
       throw new HttpException(
         {
-          status: 'error',
+          status: "error",
           service: SERVICE_NAME,
           timestamp: new Date().toISOString(),
-          error: error instanceof Error ? error.message : 'database unreachable',
+          error:
+            error instanceof Error ? error.message : "database unreachable",
         },
         HttpStatus.SERVICE_UNAVAILABLE,
       );