feat: add dark mode support

[aidandaly24]

Summary

This PR adds dark mode support to the CLI dashboard as requested in #2.

Changes

New Features

• Light and Dark Color Palettes: Added LIGHT_PALETTE and DARK_PALETTE with semantic color definitions for status, interactive, text, and border colors
• ThemeContext: Created a React context for managing theme state throughout the application
• System Color Scheme Detection: Automatically detects system color scheme preference using environment variables (COLORFGBG, COLOR_SCHEME)
• Theme Preference Options: Users can configure theme preference as light, dark, or system

Files Modified

• src/cli/tui/theme.ts - Expanded with light/dark palettes and detection utilities
• src/cli/tui/context/ThemeContext.tsx - New file for theme context and provider
• src/cli/tui/context/index.ts - Export new theme context
• src/cli/tui/App.tsx - Wrapped app with ThemeProvider
• src/cli/tui/context/__tests__/ThemeContext.test.tsx - Comprehensive tests

Usage

Components can now use the useTheme hook to access theme-aware colors:

import { useTheme } from './context';

function MyComponent() {
  const { colors, mode, setPreference } = useTheme();
  
  return (
    <Box>
      <Text color={colors.text.primary}>Hello</Text>
      <Text color={colors.status.success}>Success!</Text>
    </Box>
  );
}

Backward Compatibility

The existing STATUS_COLORS, INTERACTIVE_COLORS, TEXT_COLORS, and THEME exports are preserved (marked as deprecated) to allow gradual migration of existing components.

Testing

Added comprehensive tests for:

• ThemeProvider with different initial preferences
• useTheme hook behavior inside and outside provider
• System color scheme detection from environment variables
• Color palette structure validation

Closes #2

[github-actions]

Coverage Report

Status	Category	Percentage	Covered / Total
🔵	Lines	43.13%	3869 / 8970
🔵	Statements	42.7%	4080 / 9553
🔵	Functions	44.56%	755 / 1694
🔵	Branches	44.98%	2558 / 5686

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