Update documentation to reflect current Client-Server architecture and implementation status

[Copilot]

This PR comprehensively updates all documentation in the SharpCAT repository to accurately reflect the current state of the Client-Server architecture and removes outdated references.

Changes Made

Main README.md Updates

• Modernized project description: Replaced informal "ideas" disclaimer with professional description of SharpCAT as a .NET Standard 2.0 CAT control library
• Added comprehensive architecture documentation: Clear breakdown of core components, current implementation status, and planned features
• Enhanced usage examples: Added detailed code examples showing how to use SharpCAT class, Serial communication, radio models, CTCSS tones, and DCS codes
• Clarified Client-Server status: Honestly documented that SerialClient and SerialServer are placeholder implementations for planned future functionality
• Updated development roadmap: Replaced outdated TODO list with structured roadmap showing completed ✅ and planned 🚧 features
• Added repository structure diagram: Visual guide to help developers navigate the codebase
• Improved build instructions: Maintained existing accurate build steps while enhancing context

VirtualSerial2/README.md Updates

• Added context note: Clarified that the Windows driver sample is reference material, not integrated with the main SharpCAT library

Key Improvements

The documentation now provides:

• Honest status reporting: Clear distinction between implemented features (serial communication, radio abstractions) and planned features (client-server architecture)
• Practical usage guidance: Real code examples that developers can use immediately
• Professional presentation: Transformation from personal project notes to library documentation
• Accurate expectations: Users understand what works now vs. what's planned for the future

Technical Verification

• Project builds successfully with 0 warnings and 0 errors
• All existing functionality remains unchanged
• Documentation grew from ~94 lines to 219 lines with substantial improvements in clarity and usefulness

The SharpCAT library now has documentation that accurately represents its current capabilities while being transparent about the planned client-server architecture that motivated this update.

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