Add backend API for personal finance management application

- Introduced a comprehensive backend API using TypeScript, Fastify, and PostgreSQL.
- Added essential files including architecture documentation, environment configuration, and Docker setup.
- Implemented RESTful routes for managing assets, liabilities, clients, invoices, and cashflow.
- Established a robust database schema with Prisma for data management.
- Integrated middleware for authentication and error handling.
- Created service and repository layers to adhere to SOLID principles and clean architecture.
- Included example environment variables for development, staging, and production setups.

backend-api/src/controllers/DashboardController.ts

@@ -0,0 +1,17 @@
+import {FastifyRequest, FastifyReply} from 'fastify';
+import {DashboardService} from '../services/DashboardService';
+import {getUserId} from '../middleware/auth';
+
+/**
+ * Controller for Dashboard endpoints
+ */
+export class DashboardController {
+  constructor(private dashboardService: DashboardService) {}
+
+  async getSummary(request: FastifyRequest, reply: FastifyReply) {
+    const userId = getUserId(request);
+    const summary = await this.dashboardService.getSummary(userId);
+
+    return reply.send(summary);
+  }
+}