fix: Response wrapping, error logging, and controller hardening (COA 3)

- HttpExceptionFilter: Log actual error details for non-HttpExceptions (was silently swallowing 500s)
- ServersService: Return null fields instead of 404 for new licenses without servers
- NotificationsController: Wrap config responses as { config } to match frontend expectations
- WebstoreController: Wrap config responses as { config } to match frontend expectations
- ChatController: Replace ParseIntPipe with manual parseInt (400 on missing optional param)
- WipesController: Same ParseIntPipe fix for history limit param

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

backend-nest/src/common/filters/http-exception.filter.ts

@@ -4,14 +4,18 @@ import {
   ArgumentsHost,
   HttpException,
   HttpStatus,
+  Logger,
 } from '@nestjs/common';
 import { Response } from 'express';
 
 @Catch()
 export class HttpExceptionFilter implements ExceptionFilter {
+  private readonly logger = new Logger('ExceptionFilter');
+
   catch(exception: unknown, host: ArgumentsHost) {
     const ctx = host.switchToHttp();
     const response = ctx.getResponse<Response>();
+    const request = ctx.getRequest();
 
     let status = HttpStatus.INTERNAL_SERVER_ERROR;
     let message = 'Internal server error';
@@ -28,6 +32,13 @@ export class HttpExceptionFilter implements ExceptionFilter {
           message = obj.message[0] as string;
         }
       }
+    } else {
+      // Log non-HttpException errors with full details
+      const err = exception instanceof Error ? exception : new Error(String(exception));
+      this.logger.error(
+        `Unhandled exception on ${request.method} ${request.url}: ${err.message}`,
+        err.stack,
+      );
     }
 
     response.status(status).json({ message });