Add comprehensive Nix development documentation

## Summary
Created extensive documentation for Nix development on macOS, capturing real-world experiences and solutions.

## Documentation Added

### Context Documentation (`.claude/context/`)
- **dotfiles-architecture.md** - Repository structure and configuration hierarchy
- **nix-darwin-patterns.md** - Common patterns and best practices
- **repository-workflows.md** - Development procedures and daily workflows
- **mcp-servers.md** - MCP server system documentation

### Development Guides (`.claude/guides/`)
- **nix-development-macos.md** - Essential concepts, workflow, and advanced topics
- **nix-troubleshooting.md** - Common issues and their solutions
- **nix-module-development.md** - How to create custom Nix modules
- **lessons-learned-nix.md** - Real-world experiences from our session
- **nix-quick-reference.md** - Quick command reference and patterns

### Index Update
- Updated `.claude/index.md` with new documentation structure
- Added task-based quick references
- Marked essential docs with ⭐

## Key Topics Covered
- PATH configuration issues and solutions
- Pre-commit hook failures and fixes
- Module development patterns
- Debugging techniques
- Repository organization
- Platform-specific considerations

## Benefits
- Reduced onboarding time for new contributors
- Centralized troubleshooting knowledge
- Clear development patterns established
- Real-world solutions documented