Add comprehensive codebase documentation (CLAUDE.md)

[xorpaul]

Summary

This PR adds a comprehensive developer guide (CLAUDE.md) that documents the g10k codebase structure, architecture, and development practices. This guide serves as a reference for developers working on the project and provides context for AI-assisted development.

Key Changes

• New file: CLAUDE.md — A 381-line developer guide covering:
  • Project overview and key differentiators from r10k
  • Complete repository structure with file descriptions
  • Detailed documentation of all major source files and their responsibilities
  • Core data structures and their fields
  • Development workflow and build instructions
  • Testing patterns (config tests, crash tests, integration tests, HTTP mocks)
  • Code conventions (logging, error handling, concurrency, module installation modes)
  • CLI flags reference table
  • Quick lookup table for where to make specific changes
  • CI/CD pipeline documentation
  • Dependency reference

Notable Details

• Includes practical examples of testing patterns used in the codebase (subprocess testing for fatal conditions, hashdeep integration tests, HTTP mocks)
• Documents the strict naming convention for config tests (TestConfigXxx → tests/TestConfigXxx.yaml)
• Provides a comprehensive CLI flags reference with defaults and purposes
• Explains the three module installation modes (hardlinks, move, clone) and their use cases
• Documents the logging hierarchy and when each logging function should be used
• Includes a "Where to Make Changes" quick reference table for common development tasks

This documentation improves developer onboarding and provides a single source of truth for codebase architecture and conventions.

https://claude.ai/code/session_01Xrzb4i425wBHwFutHicJd5

[jay7x]

I see no issue merging this. Just need to keep it up-to-date with changes we made in "old school manual way" :)