[GUI] Split shared theme into resource dictionaries

[freakdaniel]

Motivation

This is the next part after #666 for #606

App.axaml currently contains the shared colors, brushes, control theme and all global style selectors in one file. This makes styling changes harder to navigate and review

This PR only reorganizes the existing theme definitions. It intentionally does not change the launcher layout, visuals or runtime behavior

Changes

• Moved shared colors and brushes into Themes/Tokens.axaml
• Moved the SettingRow control theme into Themes/Templates/SettingRow.axaml
• Split global styles into focused resource files:
  • Base.axaml
  • Surfaces.axaml
  • Buttons.axaml
  • Inputs.axaml
  • Console.axaml
  • Library.axaml
• Reduced App.axaml to the application theme composition root
• Preserved the existing resource values, selectors and style include order
• No navigation, view, localization or launcher logic changes are included

Testing

• dotnet build SharpEmu.slnx -c Release --no-restore
• dotnet test SharpEmu.slnx -c Release --no-build all 717 tests passed
• Game testing: Dream Sarah, but here are no emulator runtime or game compatibility code was changed

Checklist

By submitting this pull request, i confirm that:

• I have read and followed CONTRIBUTING.md.
• I tested my changes or marked the testing section as N/A.
• I wrote this pull request description myself and did not paste AI-generated explanations.
• I listed the game(s) I tested (or marked the testing section as N/A).

[github-actions]

📦 Build artifacts — 08dacc0

Platform	Download
Windows (win-x64)	sharpemu-win-x64-9ae1fea
Linux (linux-x64)	sharpemu-linux-x64-9ae1fea
macOS (osx-x64)	sharpemu-osx-x64-9ae1fea

From build run #1428. Downloads require a GitHub login and expire after 90 days.