feat: Add comprehensive light theme and theme switcher

✨ Features:
- Complete light theme with improved color palette
- Theme switcher in header with sun/moon icons
- Theme persistence using localStorage
- Smooth transitions between themes

🎨 Theme Improvements:
- Softer, easier-on-eyes light theme colors
- Fixed text contrast issues across all components
- Enhanced member card and tab text readability
- Fixed hover effects that made text disappear
- Improved member overlay header and body styling

🔧 Technical Implementation:
- CSS variables system for easy theme management
- JavaScript ThemeManager class for theme switching
- Responsive design for mobile devices
- Comprehensive hover state fixes
- Z-index solutions for text visibility

📱 Components Fixed:
- Member cards (hostname, IP, latency, details)
- Navigation tabs and content
- Task summaries and progress items
- Capability forms and API endpoints
- Member overlay popup
- Form inputs and dropdowns
- Status indicators and label chips

🎯 Accessibility:
- WCAG AA contrast compliance
- Proper color hierarchy
- Clear visual feedback
- Mobile-responsive design

Files added:
- public/styles/theme.css - Theme system and variables
- public/scripts/theme-manager.js - Theme management logic
- THEME_README.md - Comprehensive documentation
- THEME_IMPROVEMENTS.md - Improvement details

Files modified:
- public/index.html - Added theme switcher and script includes
- public/styles/main.css - Updated to use CSS variables

THEME_IMPROVEMENTS.md

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+# Theme Improvements - Better Contrast and Readability
+
+## Issues Fixed
+
+### 1. **Too Bright Light Theme**
+- **Before**: Very bright white backgrounds that were harsh on the eyes
+- **After**: Softer, more muted backgrounds using `#f1f5f9`, `#e2e8f0`, and `#cbd5e1`
+
+### 2. **Poor Text Contrast**
+- **Before**: Many text elements had the same color as background, making them invisible
+- **After**: Strong contrast with dark text (`#0f172a`, `#1e293b`, `#334155`) on light backgrounds
+
+### 3. **Specific Text Color Issues Fixed**
+- Member hostnames and IPs now use `var(--text-primary)` for maximum readability
+- Latency labels and values have proper contrast
+- Navigation tabs are clearly visible in both themes
+- Form inputs and dropdowns have proper text contrast
+- Status indicators have appropriate colors with good contrast
+
+## Color Palette Updates
+
+### Light Theme (Improved)
+- **Background**: Softer gradients (`#f1f5f9` → `#e2e8f0` → `#cbd5e1`)
+- **Text Primary**: `#0f172a` (very dark for maximum contrast)
+- **Text Secondary**: `#1e293b` (dark gray)
+- **Text Tertiary**: `#334155` (medium gray)
+- **Text Muted**: `#475569` (lighter gray)
+- **Borders**: Stronger borders (`rgba(30, 41, 59, 0.2)`) for better definition
+
+### Dark Theme (Unchanged)
+- Maintains the original dark theme for users who prefer it
+- All existing functionality preserved
+
+## Technical Improvements
+
+### CSS Specificity
+- Added `!important` rules for critical text elements to ensure they override any conflicting styles
+- Used `[data-theme="light"]` selectors for theme-specific overrides
+
+### Contrast Ratios
+- All text now meets WCAG AA contrast requirements
+- Status indicators have clear, distinguishable colors
+- Interactive elements have proper hover states
+
+### Readability Enhancements
+- Removed problematic opacity values that made text invisible
+- Ensured all form elements have proper text contrast
+- Fixed dropdown options to be readable
+- Improved error and success message visibility
+
+## Testing
+
+To test the improvements:
+
+1. Open `http://localhost:8080` in your browser
+2. Click the theme toggle to switch to light theme
+3. Verify all text is clearly readable
+4. Check that the background is not too bright
+5. Test form interactions and dropdowns
+6. Verify status indicators are clearly visible
+
+## Files Modified
+
+- `public/styles/theme.css` - Updated color palette and added contrast fixes
+- `public/styles/main.css` - Fixed text color issues and opacity problems
+
+The light theme is now much easier on the eyes with proper contrast for all text elements.