fix: Replace socket.io with native WS adapter — fixes WebSocket 1006

Frontend uses native WebSocket API, backend was using socket.io which
speaks an incompatible protocol. Switched to @nestjs/platform-ws so
both sides speak native WebSocket. Also fixed JWT TTL override in
docker-compose.yml (was hardcoded to 900s, now 14400s/4h).

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

backend-nest/src/main.ts

@@ -1,6 +1,7 @@
 import { NestFactory } from '@nestjs/core';
 import { ValidationPipe } from '@nestjs/common';
 import { SwaggerModule, DocumentBuilder } from '@nestjs/swagger';
+import { WsAdapter } from '@nestjs/platform-ws';
 import { AppModule } from './app.module';
 import { HttpExceptionFilter } from './common/filters/http-exception.filter';
 import { TransformInterceptor } from './common/interceptors/transform.interceptor';
@@ -8,6 +9,9 @@ import { TransformInterceptor } from './common/interceptors/transform.intercepto
 async function bootstrap() {
   const app = await NestFactory.create(AppModule);
 
+  // Use native WebSocket adapter (not socket.io)
+  app.useWebSocketAdapter(new WsAdapter(app));
+
   // Global prefix — all routes under /api
   app.setGlobalPrefix('api');