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/project-structure.mdc

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+---
+alwaysApply: true
+---
+
+# Project Structure Rules
+
+1. Backend:
+   - [src/services/](mdc:src/services/) - ALL database access
+   - [src/app/api/](mdc:src/app/api/) - API routes using services
+
+2. Frontend:
+   - [src/clients/](mdc:src/clients/) - HTTP clients
+   - [src/components/](mdc:src/components/) - React components (organized by domain)
+   - [src/hooks/](mdc:src/hooks/) - React hooks
+
+3. Shared:
+   - [src/lib/](mdc:src/lib/) - Types and utilities
+   - [scripts/](mdc:scripts/) - Utility scripts
+
+Key Files:
+
+- [src/services/database.ts](mdc:src/services/database.ts) - Database pool
+- [src/clients/base/http-client.ts](mdc:src/clients/base/http-client.ts) - Base HTTP client
+- [src/lib/types.ts](mdc:src/lib/types.ts) - Shared types
+
+❌ FORBIDDEN:
+
+- Database access outside src/services/
+- HTTP calls outside src/clients/
+- Business logic in src/components/