Optimize Claude Code integration with CLAUDE.md consolidation and /gh skill

- Reduce CLAUDE.md from 530 → 90 lines (83% reduction) by removing general
  Android/Kotlin knowledge, keeping only project-specific context
- Add repository-specific /gh skill for GitHub operations (PR creation,
  CI checks, issue management)
- Create comprehensive developer guide covering Claude Code setup and
  workflow best practices

Author: DavDo