Improve JavaScript test coverage (currently at 10.75%)

## Current State

The JavaScript test suite shows only **10.75% overall statement coverage**, with several critical components completely untested. While the testing infrastructure is well-designed, the actual coverage needs significant improvement.

## Test Coverage Breakdown

### ✅ Well-Tested Components (100% coverage)
- `platform-utils.js` - Platform detection utilities
- `shortcut-key.js` - Keyboard shortcut functionality

### ⚠️ Partially Tested Components
- `command-data.js` - 6.6% coverage (only 13 of 196 lines tested)
- `fix-line-length.js` - 55.68% coverage (scripts directory)
- `teaching.js` - 1.2% coverage (only 3 of 250 lines tested)

### ❌ Untested Components (0% coverage)
- `command-palette.js` - Core search/command functionality
- `main.js` - Main application logic

## Strengths of Current Testing Approach

1. **Well-structured testing patterns**
- Dual-file approach separating behavioral tests from implementation tests
- Comprehensive browser API mocking in `setup.js`
- Good test isolation with proper cleanup

2. **Quality test infrastructure**
- Thorough DOM manipulation testing
- Platform-specific behavior testing
- Error scenario coverage

## Areas Requiring Improvement

### 1. Critical UI Components
The command palette and main application logic have zero test coverage. These are core user-facing features that should be thoroughly tested.

### 2. Search Functionality
The command palette search functionality using Fuse.js needs comprehensive testing including:
- Search result accuracy
- Keyboard navigation
- Filter functionality
- Edge cases (empty results, special characters)

### 3. Theme Toggle System
While the infrastructure exists, the actual theme switching logic needs testing:
- Theme persistence
- Cross-page theme consistency
- Theme toggle UI interactions

### 4. Teaching Module
With only 1.2% coverage, the course sorting and filtering functionality remains largely untested.

## Recommended Actions

1. **Priority 1: Test Critical User Paths**
- Command palette opening/closing
- Search functionality
- Keyboard navigation
- Theme switching

2. **Priority 2: Increase Coverage of Partially Tested Files**
- Complete testing of `command-data.js` event handlers
- Test remaining `fix-line-length.js` edge cases
- Add tests for `teaching.js` course management

3. **Priority 3: Add Integration Tests**
- Test complete user workflows
- Test cross-component interactions
- Add visual regression tests for theme switching

## Target Coverage Goals

- **Short-term (1 month)**: Achieve 50% overall coverage
- **Medium-term (3 months)**: Achieve 70% overall coverage
- **Long-term**: Maintain 80%+ coverage with CI/CD enforcement

## Benefits of Improved Coverage

1. **Reduced regression risk** during feature development
2. **Faster debugging** with comprehensive test cases
3. **Better documentation** through test examples
4. **Increased confidence** in deployments

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*This issue was identified during test suite analysis. The current test infrastructure is solid, but needs expansion to cover critical user-facing functionality.*