Refactor: Improve code quality and consistency across profile management and error handling

[ppikrorngarn]

This PR focuses on improving code quality, consistency, and maintainability throughout the codebase. The changes include:

• Enhanced profile management with input validation and standardized error messages
• Improved HTTP error message sanitization to prevent information leakage
• Refactored CLI flag handling to reduce code duplication
• Added comprehensive unit tests for profile key parsing and building
• Standardized internal error wrapping for better debugging
• Removed unused API key flag state
• Removed unused CLI help constants to reduce clutter
• Consistent validation of provider support during profile creation