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.

docker-compose.yml

@@ -0,0 +1,66 @@
+version: '3.8'
+
+services:
+  # Development database
+  db-dev:
+    image: postgres:16-alpine
+    container_name: wealth-db-dev
+    environment:
+      POSTGRES_USER: wealth
+      POSTGRES_PASSWORD: wealth_dev
+      POSTGRES_DB: wealth_dev
+    ports:
+      - "5432:5432"
+    volumes:
+      - postgres_dev_data:/var/lib/postgresql/data
+    healthcheck:
+      test: ["CMD-SHELL", "pg_isready -U wealth -d wealth_dev"]
+      interval: 10s
+      timeout: 5s
+      retries: 5
+
+  # Staging database
+  db-staging:
+    image: postgres:16-alpine
+    container_name: wealth-db-staging
+    environment:
+      POSTGRES_USER: wealth
+      POSTGRES_PASSWORD: ${STAGING_DB_PASSWORD:-wealth_staging}
+      POSTGRES_DB: wealth_staging
+    ports:
+      - "5433:5432"
+    volumes:
+      - postgres_staging_data:/var/lib/postgresql/data
+    healthcheck:
+      test: ["CMD-SHELL", "pg_isready -U wealth -d wealth_staging"]
+      interval: 10s
+      timeout: 5s
+      retries: 5
+
+  # Production database
+  db-prod:
+    image: postgres:16-alpine
+    container_name: wealth-db-prod
+    environment:
+      POSTGRES_USER: wealth
+      POSTGRES_PASSWORD: ${PROD_DB_PASSWORD:?PROD_DB_PASSWORD is required}
+      POSTGRES_DB: wealth_prod
+    ports:
+      - "5434:5432"
+    volumes:
+      - postgres_prod_data:/var/lib/postgresql/data
+    healthcheck:
+      test: ["CMD-SHELL", "pg_isready -U wealth -d wealth_prod"]
+      interval: 10s
+      timeout: 5s
+      retries: 5
+    deploy:
+      resources:
+        limits:
+          memory: 1G
+
+volumes:
+  postgres_dev_data:
+  postgres_staging_data:
+  postgres_prod_data:
+