Remove external Google Fonts dependency from Blazor host page

[Copilot]

Removes the render-blocking Google Fonts stylesheet from the Blazor host page and uses platform-local fonts for the Blazor UI.

• What changed

  • Removed the Google Fonts stylesheet link from JournalApp/wwwroot/index.html
  • Switched the splash/loading text to a platform font stack in JournalApp/wwwroot/app.css
  • Set MudBlazor's default typography to the same platform font stack in JournalApp/Pages/MainLayout.razor

• Why

  • Avoids a startup network dependency on fonts.googleapis.com / fonts.gstatic.com
  • Avoids blocking early WebView rendering on a remote stylesheet request
  • Keeps the optimization honest: MAUI AddFont registers Roboto-Regular.ttf for MAUI controls, but it does not expose that font as a CSS web font inside Blazor's wwwroot

• Validation

  • dotnet test F:\source\repos\JournalApp\JournalApp.sln --no-restore
    • Passed: 188
    • Skipped: 1
    • Failed: 0

Refs #91.

[danielchalmers]

After reconsidering this in the context of #91 and the product requirement that the app should use Roboto on all platforms, I do not think we should merge this PR as the startup optimization.

Why:

• The Android launch logs point to much larger measured startup costs in database preparation and seeding, especially the EF pending migration check and category/debug seed paths.
• This font change is speculative by comparison; we do not have evidence from the launch logs that Google Fonts is a material part of the multi-second splash delay.
• On Android specifically, Roboto is already the platform font, so removing the Google Fonts request is unlikely to be the change that materially fixes Android startup responsiveness.
• On non-Android platforms, removing the Google Fonts stylesheet without adding a web-visible local @font-face means the Blazor WebView no longer reliably uses Roboto. My follow-up system-font-stack commit makes that behavior explicit, but it conflicts with the stated goal of using Roboto everywhere.

Recommendation: close this PR without merging. If we later want to remove the network dependency while preserving Roboto across all platforms, that should be a separate self-hosted-font PR that adds the needed Roboto web font assets under wwwroot and wires them with @font-face. For #91, the next optimization work should stay focused on the measured startup database costs.