Add comprehensive XML documentation to CAT/CI-V command model implementations and infrastructure

[Copilot]

This PR adds extensive XML documentation comments to all classes, interfaces, and public members across the SharpCAT library, providing comprehensive guidance for both users and developers working with ham radio CAT (Computer Aided Transceiver) and CI-V (Computer Interface V) protocols.

Key Documentation Improvements

Protocol Distinction

Clear documentation now distinguishes between the two main protocols:

• CAT Protocol: ASCII-based commands used by Yaesu radios (FT-818, FT-991A, etc.)
• CI-V Protocol: Binary protocol used by Icom radios (ID-4100A, IC-7300, etc.)
• Kenwood: Protocol considerations documented for future implementation

Core Infrastructure

• SharpCAT: Main library class with protocol explanations, CTCSS/DCS tone definitions, and serial port management
• Serial Communications: Complete documentation of serial port configuration, event handling, and radio-specific timeouts
• Command Structures: Detailed explanations of CATCommand (ASCII) vs CIVCommand (binary) with examples

Radio Implementations

• Yaesu FT-818: Complete CAT implementation with all command codes, parameter explanations, and usage examples
• Icom ID-4100A: CI-V implementation with D-STAR capabilities and response pattern documentation
• Kenwood TH-D74A: Placeholder with comprehensive specifications for future implementation

Developer Guidance

• Ham radio terminology explanations for developers unfamiliar with CAT/CI-V
• Command construction examples and expected radio responses
• Safety warnings for PTT and power control operations
• Extension patterns for adding new radio models

Example Documentation Quality

/// <summary>
/// Generates the CAT command to set the operating frequency on the FT-818.
/// </summary>
/// <param name="freq">The frequency in Hertz (e.g., 14205000.0 for 14.205 MHz)</param>
/// <returns>Properly formatted CAT command string</returns>
/// <remarks>
/// The FT-818 frequency command format uses 8-digit BCD encoding.
/// Example: 14.205 MHz (14205000 Hz) should become "014205000" in the CAT command.
/// </remarks>

This documentation enables developers to:

• Understand the differences between CAT and CI-V protocols
• Implement new radio models following established patterns
• Use the library effectively without deep ham radio knowledge
• Extend functionality with confidence in the expected interfaces

All classes now have comprehensive XML documentation covering purpose, parameters, usage, and radio-specific implementation details.

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