improvement/1049: Refactor Exceptions to Use Base Initializer

[babakjahan]

Summary

Refactor the exception hierarchy to remove custom init methods from individual exception classes and rely on AppBaseException for all initialization logic.

Problem

Current exception classes duplicate constructor logic, making the code harder to maintain and extend.

Proposed Change

Move all initialization logic to AppBaseException

Define defaults (default_error_code, default_message, default_status_code) at the class level

Remove init methods from child exceptions (InternalServerException, BadRequestException, etc.)

Acceptance Criteria

• No child exception defines init
• Behavior remains backward compatible
• Code is simpler and consistent