Add Architecture Guide and API Examples for Developer Onboarding

[SpIob]

After reviewing existing issues and community discussions, I've found that new contributors often struggle with:

1. Understanding the overall system architecture before diving into code
2. Finding practical, working examples of Console API usage
3. Knowing which design patterns are used throughout the codebase
4. Understanding the data flow between components (TerminalApp → TerminalControl → TerminalCore → ConPTY → conhost.exe)

The current documentation lacks architectural guidance and real-world API examples that would help developers get productive faster.

Proposed Solution

Add two new markdown documents to the /doc folder:

1. ARCHITECTURE.md

This document would cover:

• High-level system architecture with component diagrams
• Component relationships (TerminalApp, TerminalControl, TerminalCore, Console Host)
• Data flow for input and output processing
• Key design patterns used in the codebase (Separation of Concerns, Observer Pattern, Factory Pattern, Dependency Injection)
• Threading model and thread safety guidelines
• Memory management best practices (RAII, smart pointers)
• Extensibility points for custom connections and renderers
• Performance and security considerations

2. API_EXAMPLES.md

This document would provide copy-paste-ready examples for:

• Basic console output (WriteConsole, C++ streams)
• Console colors and attributes (16-color, 256-color, RGB true color)
• Cursor control operations
• Buffer read/write operations
• Keyboard and mouse input handling
• Virtual Terminal sequence processing
• Pseudoconsole (ConPTY) creation and usage
• Advanced scenarios (progress bars, interactive menus, colored logging)

Benefits

• Faster Contributor Onboarding: New developers can understand the architecture before navigating thousands of source files
• Reduced Support Burden: Common questions about architecture and API usage will be answered in documentation
• Better Code Quality: Understanding design patterns leads to contributions that follow established patterns
• Improved API Adoption: External developers building terminal applications will have working examples to reference

Implementation Plan

• Create doc/ARCHITECTURE.md with system overview and component diagrams
• Create doc/API_EXAMPLES.md with practical code examples
• Update README.md Documentation section with links to new guides
• Cross-reference existing docs (ORGANIZATION.md, building.md, TAEF.md) where appropriate