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/DebtCategoryService.ts

@@ -1,5 +1,5 @@
 import {DebtCategory} from '@prisma/client';
-import {DebtCategoryRepository} from '../repositories/DebtCategoryRepository';
+import {DebtCategoryRepository, DebtCategoryWithStats} from '../repositories/DebtCategoryRepository';
 import {NotFoundError, ValidationError, ForbiddenError, ConflictError} from '../utils/errors';
 
 export interface CreateDebtCategoryDTO {
@@ -84,7 +84,7 @@ export class DebtCategoryService {
   /**
    * Get categories with statistics
    */
-  async getWithStats(userId: string): Promise<any[]> {
+  async getWithStats(userId: string): Promise<DebtCategoryWithStats[]> {
     return this.categoryRepository.getWithStats(userId);
   }
 
@@ -128,7 +128,7 @@ export class DebtCategoryService {
    * Delete a category
    */
   async delete(id: string, userId: string): Promise<void> {
-    const category = await this.getById(id, userId);
+    await this.getById(id, userId);
 
     // Check if category has accounts
     // Note: Cascade delete will remove all accounts and payments