feat: Solar high-contrast theme for outdoor laptop use (Closes #14)

[Jokay1997]

Summary

Implements a specialized Solar high-contrast theme for field engineers inspecting outdoor mesh network nodes under direct sunlight. The theme achieves a minimum 10:1 contrast ratio for all text elements and passes WCAG 2.2 AAA compliance.

Changes

New Files

• *\src/styles/themes/solar.css* - Solar theme CSS custom properties with verified 10:1+ contrast ratios
• *\src/hooks/useTheme.ts* - Theme hook with \localStorage\ persistence and system preference detection
• *\src/components/providers/ThemeProvider.tsx* - React context provider for theme state
• *\src/components/settings/ThemeSelector.tsx* - Theme toggle UI (Light / Dark / High Contrast (Solar))
• *\scripts/check-contrast.mjs* - CI script that validates all CSS variable contrast pairs meet thresholds

Modified Files

• *\�pp/globals.css* - Added .solar\ and .dark\ class variables; defined semantic CSS custom properties for all modes; added 3px solid focus ring styles
• *\�pp/layout.tsx* - Added blocking inline script to read \localStorage\ and apply theme class before first paint (prevents FOUC)
• *\�pp/providers.tsx* - Wrapped component tree with \ThemeProvider\
• *\�pp/page.tsx* - Migrated all hardcoded Tailwind arbitrary colors to semantic CSS variable classes
• *.github/workflows/test.yml* - Added contrast audit step to CI pipeline

Solar Theme Contrast Verification

All Solar theme color pairs verified at ≥10:1:

• Text on background: 21:1 (pure black on pure white)
• Primary (#0022CC) on background: 10:1
• Focus ring (pure black) on background: 21:1 (3px solid)
• All interactive, success, warning, danger states also meet ≥10:1
• Non-color information conveyed via patterns/icons for colorblind users

Closes #14