fix: resolve theme-switching crash and add automated UI action tests across all tabs - #55

Summary of Changes

• Theme Switching Crash Fix:
  • Identified root cause of crash when switching framework theme styles: dynamically modifying \Current.Styles\ (\Styles.Clear()) broke visual trees containing Avalonia 11 \ScrollViewer\ controls.
  • Converted \SetThemeStyle\ in both Desktop (\App.axaml.cs) and Web (\LocalLLMServerManager.Web/App.axaml.cs) to a safe non-destructive implementation that keeps base design system styles intact and cleanly toggles theme palettes (\MatteCarbon\ vs. \OledBlack) via \ThemeService.
  • Added UI thread dispatch verification in \ThemeService.SetTheme\ to prevent thread affinity violations when invoked from non-UI threads.
  • Added cross-assembly resolution in \SettingsViewModel.SwitchThemeStyle\ supporting Desktop, Web, and headless test runners.
• Automated Headless UI Action Tests:
  • Added full interaction tests across all UI tabs, pickers, and actions in \AvaloniaHeadlessInteractionTests.cs:
    • Settings tab: dynamic theme ComboBox, framework theme buttons, tool discovery, status refresh, video/audio pack toggles, and preset manager actions (create, filter, reset, JSON export/import).
    • Telemetry header: status refresh and hardware telemetry readouts.
    • Engine Studio tab: Test Flight modal toggle, engine selectors, and preset bar controls.
    • Ollama tab: context token slider, VRAM unload, filter pills, and model deletion confirmation flow.
    • Hub tabs (HuggingFace & Civitai): search queries, modality presets, filter tags, and VRAM fit verdict filters.
  • Switched \StudioControlInstantiationTests\ to [AvaloniaFact]\ for proper UI dispatcher affinity.
• WASM Sync:
  • Synced compiled WebAssembly distribution binaries in \wwwroot/_framework/.

Verification

• Headless UI tests: \20 passed, 0 failed.
• Solution test suite: \584 passed, 0 failed\ (1 skipped doc screenshot generator).
• Linter:
  pm run lint\ passed with 0 errors.
• Typechecker:
  px tsc --noEmit\ passed with 0 errors.