feat: migrate Zsh to new feature folder architecture

[ooloth]

Summary

Migrate Zsh configuration and management to the new self-contained feature structure, following the established pattern from features like git/, homebrew/, ssh/, and tmux/.

This migration transforms the existing bin/install/zsh.zsh script into a comprehensive, self-contained feature with improved maintainability, testability, and consistency.

Changes

🏗️ New Feature Structure

• features/zsh/install.bash - Zsh installation and shell configuration (converted from Zsh to Bash)
• features/zsh/update.bash - Zsh updates via Homebrew with validation
• features/zsh/utils.bash - Self-contained utility functions for Zsh management
• features/zsh/config/ - Complete Zsh configuration files (copied from config/zsh/)
• features/zsh/tests/ - Comprehensive test suite using BATS framework
• features/zsh/README.md - Detailed feature documentation

🔧 Self-Contained Design

• ✅ No external dependencies on bin/lib/ utilities
• ✅ Self-contained utility functions for installation and validation
• ✅ Bash-based scripts (converted from original Zsh for consistency)
• ✅ Comprehensive error handling and graceful failure recovery
• ✅ Machine detection integration for work-specific configurations

📦 Installation Features

• ✅ Installs Zsh via Homebrew if not present
• ✅ Automatically adds Zsh to /etc/shells
• ✅ Changes user default shell to Zsh with validation
• ✅ Validates installation and configuration integrity
• ✅ Supports machine-specific configurations (work/personal)

🧪 Comprehensive Testing

• test-zsh-utils.bats - Unit tests for utility functions with mocking
• test-zsh-installation.bats - Integration tests for installation workflow
• test-zsh-update.bats - Update functionality testing with edge cases
• ✅ Safe testing with comprehensive mocking (no system modification)
• ✅ Tests cover success paths, error conditions, and edge cases

⚙️ Configuration Management

• ✅ Preserves all existing Zsh configuration files
• ✅ Maintains work-specific configuration support in config/work/
• ✅ Integrates with machine detection system (IS_WORK, etc.)
• ✅ Supports environment-specific settings and overrides

Benefits

🔄 Consistency

• Follows established feature architecture pattern
• Consistent with other migrated features (git/, homebrew/, etc.)
• Standardized script structure and error handling

🛡️ Reliability

• Comprehensive validation at each step
• Graceful error handling and recovery
• Safe to re-run multiple times (idempotent)

🧪 Testability

• Complete test coverage with BATS framework
• Isolated testing with mocking (no system changes during tests)
• Easy to add new tests for future functionality

📚 Maintainability

• Self-contained with clear boundaries
• Well-documented with comprehensive README
• Modular utility functions for reusability

Backward Compatibility

✅ Fully backward compatible - no breaking changes to existing functionality
✅ Configuration preserved - all existing Zsh configurations maintained
✅ Machine detection intact - work-specific configurations still applied
✅ Installation behavior unchanged - same end result as original script

Testing Strategy

# Run all Zsh feature tests
bats features/zsh/tests/

# Test installation workflow
bats features/zsh/tests/test-zsh-installation.bats

# Test utility functions
bats features/zsh/tests/test-zsh-utils.bats

# Test update functionality
bats features/zsh/tests/test-zsh-update.bats

Migration Pattern

This migration follows the established pattern used for other features:

1. ✅ Self-contained - no external bin/lib dependencies
2. ✅ Bash-based - consistent scripting language
3. ✅ Comprehensive tests - BATS framework with mocking
4. ✅ Documentation - detailed README with usage examples
5. ✅ Error handling - graceful failures and validation
6. ✅ Configuration management - organized config/ directory

Next Steps

After this PR is merged:

1. 🔄 Update main installation scripts to use new feature structure
2. 🗑️ Remove deprecated bin/install/zsh.zsh script
3. 📚 Update main README to reference new feature location
4. 🔍 Consider applying same pattern to remaining features

Test Plan

• Verify all bash scripts have valid syntax
• Run BATS test suite and ensure all tests pass
• Test installation workflow in isolated environment
• Validate configuration file preservation
• Confirm machine detection integration works
• Test update functionality with various scenarios
• Verify error handling and graceful failures
• Confirm backward compatibility with existing setup