feat: Full petmaster CRM with NestJS API and React frontend

- Client management (CRUD with JSONB custom fields)
- Pet profiles
- Service catalog with per-client pricing
- Booking calendar with recurring appointments
- Invoicing with Stripe integration
- Real-time messaging (WebSocket)
- Self-booking portal
- Staff assignment
- Docker multi-stage builds
- Prisma schema + seed

api/src/messages/messages.service.ts

@@ -0,0 +1,41 @@
+import { Injectable, NotFoundException } from '@nestjs/common';
+import { PrismaService } from '../prisma/prisma.service';
+import { SendMessageDto } from './dto/message.dto';
+
+@Injectable()
+export class MessagesService {
+  constructor(private prisma: PrismaService) {}
+
+  async getConversation(clientId: string, staffId: string) {
+    await this.prisma.client.findUniqueOrThrow({ where: { id: clientId } });
+
+    return this.prisma.message.findMany({
+      where: {
+        clientId,
+      },
+      orderBy: { createdAt: 'asc' },
+    });
+  }
+
+  async getUnreadCount(clientId: string, staffId: string) {
+    const count = await this.prisma.message.count({
+      where: {
+        clientId,
+        readAt: null,
+      },
+    });
+    return { unreadCount: count };
+  }
+
+  async markAsRead(clientId: string, messageIds: string[]) {
+    await this.prisma.client.findUniqueOrThrow({ where: { id: clientId } });
+
+    return this.prisma.message.updateMany({
+      where: {
+        id: { in: messageIds },
+        clientId,
+      },
+      data: { readAt: new Date() },
+    });
+  }
+}