Load config override from .claudesync.json

[ayushin]

Add support for local configuration overrides using .claudesync files

• Implement recursive search for .claudesync files in current and parent directories
• Override default and user configurations with values from .claudesync
• Handle relative paths in local_path setting relative to .claudesync file location
• Maintain backward compatibility with existing configuration system
• Allow for project-specific configurations without modifying global settings

This feature enables users to easily set up project-specific configurations, improving flexibility and ease of use for multi-project setups.

Solves #54