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/package.json

@@ -0,0 +1,34 @@
+{
+  "name": "personal-finances-api",
+  "version": "1.0.0",
+  "description": "Backend API for Personal Finances application",
+  "module": "src/index.ts",
+  "type": "module",
+  "private": true,
+  "scripts": {
+    "dev": "bun run --watch src/index.ts",
+    "start": "bun run src/index.ts",
+    "db:generate": "prisma generate",
+    "db:push": "prisma db push",
+    "db:migrate": "prisma migrate dev",
+    "db:studio": "prisma studio"
+  },
+  "devDependencies": {
+    "@types/bcryptjs": "^3.0.0",
+    "@types/bun": "latest",
+    "prisma": "5.22.0"
+  },
+  "peerDependencies": {
+    "typescript": "^5"
+  },
+  "dependencies": {
+    "@fastify/cors": "^11.1.0",
+    "@fastify/jwt": "^10.0.0",
+    "@fastify/swagger": "^9.6.1",
+    "@fastify/swagger-ui": "^5.2.3",
+    "@prisma/client": "5.22.0",
+    "bcryptjs": "^3.0.3",
+    "fastify": "^5.6.2",
+    "zod": "^4.1.13"
+  }
+}