Add project structure and rules documentation: Introduce guidelines for organizing backend, frontend, and shared components, including rules for services, API routes, clients, and components to ensure a consistent and maintainable codebase.

.cursor/rules/services.mdc

@@ -0,0 +1,42 @@
+---
+globs: src/services/*.ts
+---
+
+# Services Rules
+
+1. Services MUST contain ALL PostgreSQL queries
+2. Services are the ONLY layer allowed to communicate with the database
+3. Each service MUST:
+   - Use the pool from [src/services/database.ts](mdc:src/services/database.ts)
+   - Implement proper transaction management
+   - Handle errors and logging
+   - Validate data before insertion
+   - Have a clear interface
+
+Example of correct service implementation:
+
+```typescript
+export class MyService {
+  constructor(private pool: Pool) {}
+
+  async myMethod(): Promise<Result> {
+    const client = await this.pool.connect();
+    try {
+      await client.query("BEGIN");
+      // ... queries
+      await client.query("COMMIT");
+    } catch (error) {
+      await client.query("ROLLBACK");
+      throw error;
+    } finally {
+      client.release();
+    }
+  }
+}
+```
+
+❌ FORBIDDEN:
+
+- Direct database queries outside src/services
+- Raw SQL in API routes
+- Database logic in components