Standardize Error Messages and Response Formats

[Adedayo-Data]

Overview

This PR implements a centralized and standardized error-handling architecture across the PropChain-BackEnd. Previously, error responses were inconsistent in structure and message format. This refactor ensures that every endpoint returns a predictable, REST-compliant error object, improving the developer experience for frontend integration and debugging.

Changes Made Includes:

1. Centralized Error Module: Implemented a core error-handling layer in src/common/errors with custom exception classes (e.g., InvalidCredentialsException, UserNotFoundException, BusinessRuleViolationException).

2. Response Standardization: All error responses now follow a consistent template including status, message, timestamp, and category.

3. Service Integration:

    - Updated AuthService to use standardized credential validation errors.

    - Refactored PropertiesService (findOne, update, create, remove) to utilize custom exceptions and proper HTTP status codes.

4. Test Suite Alignment:

    - Updated test/auth/auth.service.spec.ts to match standardized error strings.

    - Resolved constructor mismatches and import conflicts in test/properties/properties.service.spec.ts.

    - Verified that all 266 tests (including unit, performance, and validation) are passing.

closes #49

[LaGodxy]

@Adedayo-Data resolve conflicts.

[Adedayo-Data]

Merge conflict resolved. Please resolve