feat(components/theme,i18n): add test harnesses for theme and i18n libraries

[devin-ai-integration]

feat(components/theme,i18n): add test harnesses for theme and i18n libraries

Summary

This PR adds test harnesses for two core infrastructure components that previously lacked testing support:

@skyux/theme/testing - SkyThemeHarness for testing components that use the [skyTheme] directive. Exposes methods to query theme state including getThemeName(), getThemeMode(), getThemeSpacing(), and convenience boolean methods like isModernTheme(), isDarkMode(), etc.

@skyux/i18n/testing - SkyResourcesHarness for testing elements that display localized content. Provides getText(), getInnerHtml(), and getAttribute() methods.

Both harnesses follow established patterns from existing harnesses in the codebase, extending SkyComponentHarness and implementing the standard with() filter method.

Review & Testing Checklist for Human

• Verify the i18n harness selector - The SkyResourcesHarness uses [skyLibResources],[skyAppResources] as the host selector. Confirm this matches actual usage patterns in consuming applications, as these appear to be pipe names rather than directive selectors.
• Run the test suites in CI - Tests could not be executed locally due to Chrome unavailability. Verify all tests pass in CI with actual browser execution.
• Validate theme CSS class detection - The SkyThemeHarness detects theme state by checking CSS classes (sky-theme-modern, sky-theme-mode-dark, sky-theme-modern-compact). Confirm these class names are stable and correctly applied by the theme service.
• Test harness usage in a real component test - Consider writing a quick integration test using these harnesses against an actual SKY UX component to validate the API works as expected.

Recommended test plan: After CI passes, import SkyThemeHarness and SkyResourcesHarness in an existing component test file and verify they can be instantiated and queried correctly.

Notes

• Documentation.json files were not updated because the manifest generator requires a specific format with development/testing/codeExamples sections. The harnesses are still exported and usable via the public API.
• TypeScript compilation verified locally; actual test execution pending CI.

Link to Devin run: https://app.devin.ai/sessions/40159d8b73b6471dbfc064046a58280e
Requested by: @bcmake

[devin-ai-integration]

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