Adding Demo Application Framework Integration

[mdwigley]

Description

Adds a demo application with structured DI, SDL3 window handling, and basic UI components. Includes Vacuum for service initialization and main loop, MainView and MainViewModel for UI and data context, and updates Program.cs to launch the demo.

Related Issue

• Resolves Demo Application Framework Integration #69

Motivation and Context

Provides a reference implementation for framework developers to validate DI setup, SDL3 integration, and UI component wiring.

How Has This Been Tested?

• Ensured the demo application compiles successfully.

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)
• Asset change (adds or updates icons, templates, or other assets)
• Documentation change (adds or updates documentation)
• Plugin change (adds or updates a plugin)

Checklist:

• I have read the CONTRIBUTING document.
• My change requires a change to the core logic.
  • I have linked the project issue above.
• My change requires a change to the assets.
  • I have linked the asset issue above.
• My change requires a change to the documentation.
  • I have linked the documentation issue above.
• My change requires a change to a plugin.
  • I have linked the plugin issue above.