📝 Update documentation for Studio TUI and streamline project structure

Overhaul README.md, CLAUDE.md, and CONFIG.md with comprehensive documentation
for the new Studio TUI and its six specialized modes (Explore, Commit, Review,
PR, Changelog, Release Notes).

Key documentation improvements:
- Add complete Studio keyboard navigation reference and mode switching guides
- Document chat integration with Iris and content update capabilities
- Restructure project structure to reflect Studio architecture with reducer
  pattern, event-driven state management, and component hierarchy
- Update provider configuration tables with fast_model support and current
  default models (gpt-5.1, claude-sonnet-4-5-20250929, gemini-3-pro-preview)
- Expand SilkCircuit Neon design language with background colors and RGB values
- Add troubleshooting tables and environment variable documentation
- Convert prose-heavy sections to scannable tables for better readability

Author: hyperb1iss