feat: add ticket comments, file attachments, mention notifications

- Comment module with CRUD and file upload via multer
- @mention parsing with user notification
- Assignment notification on ticket update
- Notification service enhanced with ticketId linking
- ServeStaticModule for uploaded files

src/comment/comment.controller.ts

@@ -0,0 +1,52 @@
+import {
+  Controller,
+  Get,
+  Post,
+  Param,
+  Body,
+  UseGuards,
+  UseInterceptors,
+  UploadedFiles,
+} from '@nestjs/common';
+import { AuthGuard } from '@nestjs/passport';
+import { FileFieldsInterceptor } from '@nestjs/platform-express';
+import { CommentService } from './comment.service';
+import { CreateCommentDto } from './dto/create-comment.dto';
+import { Roles } from '../common/decorators/roles.decorator';
+import { RolesGuard } from '../common/guards/roles.guard';
+import { TenantGuard } from '../common/guards/tenant.guard';
+import { CurrentUser, CurrentUserPayload } from '../common/decorators/current-user.decorator';
+import { multerOptions } from '../common/multer/multer.config';
+
+@Controller('tickets/:ticketId/comments')
+@UseGuards(AuthGuard('jwt'), TenantGuard, RolesGuard)
+export class CommentController {
+  constructor(private readonly commentService: CommentService) {}
+
+  @Get()
+  @Roles('technician')
+  async findAll(
+    @CurrentUser() user: CurrentUserPayload,
+    @Param('ticketId') ticketId: string,
+  ) {
+    return this.commentService.findAll(user.tenantId, ticketId);
+  }
+
+  @Post()
+  @Roles('technician')
+  @UseInterceptors(FileFieldsInterceptor([{ name: 'files', maxCount: 3 }], multerOptions))
+  async create(
+    @CurrentUser() user: CurrentUserPayload,
+    @Param('ticketId') ticketId: string,
+    @Body() dto: CreateCommentDto,
+    @UploadedFiles() files?: { files?: Express.Multer.File[] },
+  ) {
+    return this.commentService.create(
+      user.tenantId,
+      ticketId,
+      user.sub,
+      dto.content,
+      files?.files,
+    );
+  }
+}