Enhance ESLint configuration and improve code consistency

- Added '@typescript-eslint/no-unused-vars' rule to ESLint configuration for better variable management in TypeScript files.
- Updated database.ts to ensure consistent logging format.
- Refactored AuthController and CashflowController to improve variable naming and maintainability.
- Added spacing for better readability in multiple controller methods.
- Adjusted error handling in middleware and repository files for improved clarity.
- Enhanced various service and repository methods to ensure consistent return types and error handling.
- Made minor formatting adjustments across frontend components for improved user experience.

backend-api/src/services/ClientService.ts

@@ -1,5 +1,5 @@
 import {Client} from '@prisma/client';
-import {ClientRepository} from '../repositories/ClientRepository';
+import {ClientRepository, ClientWithStats} from '../repositories/ClientRepository';
 import {NotFoundError, ValidationError, ForbiddenError, ConflictError} from '../utils/errors';
 
 export interface CreateClientDTO {
@@ -60,7 +60,7 @@ export class ClientService {
   /**
    * Get clients with statistics
    */
-  async getWithStats(userId: string): Promise<any[]> {
+  async getWithStats(userId: string): Promise<ClientWithStats[]> {
     return this.clientRepository.getWithStats(userId);
   }
 
@@ -107,7 +107,7 @@ export class ClientService {
    */
   async delete(id: string, userId: string): Promise<void> {
     // Verify ownership
-    const client = await this.getById(id, userId);
+    await this.getById(id, userId);
 
     // Check if client has invoices - we still allow deletion due to cascade
     // but you might want to prevent deletion if there are invoices