Add System light/dark theme selection and Pale Graphite theme

[Timthreetwelve]

Add System light/dark theme selection and Pale Graphite theme

Support selecting separate light/dark themes when "System" theme is active. Add SystemLightTheme and SystemDarkTheme to user settings and update theme application logic. Introduce new "LightGray" (Pale Graphite) theme. Refactor Settings UI with new ComboBox style and conditional visibility for system theme options. Update localization and view model for new theme options.

[Copilot]

Pull request overview

Adds finer-grained theming by allowing separate light/dark theme choices when “System” is selected, and introduces a new light theme (“Pale Graphite” / LightGray). The update also refactors Settings UI styling to use a dedicated ComboBox style and updates theme application logic and localization resources.

Changes:

• Add SystemLightTheme / SystemDarkTheme settings and update theme resolution when ThemeType.System is active.
• Introduce new ThemeType.LightGray (“Pale Graphite”) and include it in theme selection and theme-cycling logic.
• Refactor Settings UI theme section (conditional light/dark theme pickers when System theme is selected) and add a shared Settings ComboBox style.

Reviewed changes

Copilot reviewed 10 out of 10 changed files in this pull request and generated 3 comments.

Show a summary per file

File	Description
GetMyIP/Views/SettingsPage.xaml	Adds conditional light/dark theme selectors for System mode and switches to a dedicated Settings ComboBox style.
GetMyIP/ViewModels/SettingsViewModel.cs	Provides curated theme lists (ThemeTypes, SystemThemeTypes) for Settings UI.
GetMyIP/ViewModels/NavigationViewModel.cs	Updates keyboard theme-cycling to include LightGray.
GetMyIP/Styles/ComboBoxStyle.xaml	Introduces SettingsComboBox style based on MaterialDesign ComboBox.
GetMyIP/Models/Enums.cs	Adds ThemeType.LightGray with localized description key.
GetMyIP/Languages/Strings.en-US.xaml	Adds new strings for Light/Dark mode theme labels and the “Pale Graphite” theme name.
GetMyIP/Helpers/MainWindowHelpers.cs	Applies SystemLightTheme/SystemDarkTheme selection logic and defines LightGray theme colors.
GetMyIP/Converters/EnumToVisibilityConverter.cs	Adds enum-to-Visibility converter for conditional UI display.
GetMyIP/Configuration/UserSettings.cs	Adds persisted settings for system light/dark theme selection.
GetMyIP/App.xaml	Merges the new ComboBox style resource dictionary.

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