feat(settings): add theme preference with system default support #158 (AI-generated)

[Gheb6]

This pull request description was written by an AI agent.

Closes #158

Summary of Changes

• Introduced ThemeProvider and ThemeContext in src/store/ThemeContext.tsx supporting system, light, and dark modes with persistence in AsyncStorage under @climbstack/theme_mode.
• Updated useThemeColors in src/utils/useThemeColors.ts to consume ThemeContext when available, falling back gracefully to useColorScheme() when outside the provider.
• Added Theme preference tile and selection modal in src/screens/SettingsScreen.tsx, matching the language selector design and accessibility conventions.
• Wrapped root application in ThemeProvider in App.tsx, and updated RootNavigator, TabNavigator, and StatusBar to dynamically adapt to the active theme.
• Added internationalization keys ( hemeTitle, selectTheme, hemeSystem, hemeLight, hemeDark) across all supported languages (en, it, de, r, es) in src/utils/i18n.ts.
• Added unit tests in src/store/tests/ThemeContext.test.tsx (100% coverage), src/utils/tests/useThemeColors.test.tsx, and updated src/screens/tests/SettingsScreen.test.tsx.

AI Generation Disclosure

• Tool / Agent: Antigravity (Google DeepMind)
• Model: Gemini 3.8 Flash
• AI-generated files:
  • src/store/ThemeContext.tsx (all lines)
  • src/store/tests/ThemeContext.test.tsx (all lines)
  • src/utils/useThemeColors.ts (all lines)
  • src/utils/tests/useThemeColors.test.tsx (all lines)
  • src/utils/i18n.ts (theme translation keys)
  • src/screens/SettingsScreen.tsx (theme tile and modal)
  • src/screens/tests/SettingsScreen.test.tsx (theme modal tests)
  • App.tsx (ThemeProvider integration)

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.

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