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.service.ts

@@ -0,0 +1,117 @@
+import { Injectable, NotFoundException } from '@nestjs/common';
+import { PrismaService } from '../prisma/prisma.service';
+import { NotificationService } from '../notification/notification.service';
+
+@Injectable()
+export class CommentService {
+  constructor(
+    private readonly prisma: PrismaService,
+    private readonly notificationService: NotificationService,
+  ) {}
+
+  async findAll(tenantId: string, ticketId: string) {
+    const db = this.prisma.forTenant(tenantId);
+    const ticket = await db.ticket.findFirst({ where: { id: ticketId } });
+    if (!ticket) throw new NotFoundException('Ticket not found');
+
+    return this.prisma.ticketComment.findMany({
+      where: { tenantId, ticketId },
+      include: {
+        author: { select: { id: true, firstName: true, lastName: true } },
+        attachments: true,
+      },
+      orderBy: { createdAt: 'asc' },
+    });
+  }
+
+  async create(
+    tenantId: string,
+    ticketId: string,
+    userId: string,
+    content: string,
+    files?: Express.Multer.File[],
+  ) {
+    const db = this.prisma.forTenant(tenantId);
+    const ticket = await db.ticket.findFirst({ where: { id: ticketId } });
+    if (!ticket) throw new NotFoundException('Ticket not found');
+
+    const comment = await this.prisma.ticketComment.create({
+      data: {
+        tenantId,
+        ticketId,
+        userId,
+        content,
+        attachments: files?.length
+          ? {
+              create: files.map((f) => ({
+                fileName: f.originalname,
+                filePath: f.filename,
+                fileType: f.mimetype,
+                fileSize: f.size,
+              })),
+            }
+          : undefined,
+      },
+      include: {
+        author: { select: { id: true, firstName: true, lastName: true } },
+        attachments: true,
+      },
+    });
+
+    // Parse @mentions and notify mentioned users
+    const mentions = this.parseMentions(content);
+    if (mentions.length > 0) {
+      const db2 = this.prisma.forTenant(tenantId);
+      const users = await db2.user.findMany({
+        where: { tenantId, isActive: true },
+        select: { id: true, firstName: true, lastName: true },
+      });
+
+      const commenterName = `${comment.author.firstName} ${comment.author.lastName}`;
+
+      for (const mention of mentions) {
+        const mentionedUser = users.find(
+          (u) =>
+            `${u.firstName} ${u.lastName}`.toLowerCase() === mention.toLowerCase() ||
+            u.firstName.toLowerCase() === mention.toLowerCase(),
+        );
+        if (mentionedUser && mentionedUser.id !== userId) {
+          await this.notificationService.create(tenantId, {
+            userId: mentionedUser.id,
+            type: 'in_app',
+            channel: 'mention',
+            title: 'You were mentioned',
+            message: `${commenterName} mentioned you in "${ticket.title}"`,
+            ticketId,
+          });
+        }
+      }
+    }
+
+    // Notify ticket creator (if not the commenter)
+    if (ticket.createdById && ticket.createdById !== userId) {
+      const commenterName = `${comment.author.firstName} ${comment.author.lastName}`;
+      await this.notificationService.create(tenantId, {
+        userId: ticket.createdById,
+        type: 'in_app',
+        channel: 'comment_added',
+        title: 'New comment on your ticket',
+        message: `${commenterName} commented on "${ticket.title}"`,
+        ticketId,
+      });
+    }
+
+    return comment;
+  }
+
+  /** Extract @FirstName or @FirstNameLastName from content */
+  private parseMentions(content: string): string[] {
+    const regex = /@(\w+(?:\s+\w+)?)/g;
+    const matches: string[] = [];
+    let match: RegExpExecArray | null;
+    while ((match = regex.exec(content)) !== null) {
+      matches.push(match[1]);
+    }
+    return [...new Set(matches)];
+  }
+}