Make StrideCleanUI the default compositor setup

This is a known issue that hasn't been making any headway. Anyone getting into UI work on their project will run into it. White being grey and other colors being dim.

I don't think new users should need to find the clean ui fix repo, try to figure it out, and fumble around when one small mistake in the editor can break things.

Suggestion: Use the StrideCleanUI setup as the default for new projects/templates.

Creates a "UserInterface" render stage using RenderGroup31
UI renders clean without post-processing effects
Works in both editor and game

For new projects: It's just there by default. Users set their UI to RenderGroup31 and it works.

For existing projects: No changes. If they want the fix they can either:

1. Do the CleanUIFix themselves
2. Copy the GraphicsCompositor.sdgfxcomp asset from a project with the fix already (assuming they haven't made changes to their default one yet)
3. Use the Community Toolkit code fix: game.AddCleanUIStage(); (This only fixes it at runtime, not in the editor during development / color grading).

Related: PR #1603 (similar approach), Community Toolkit's AddCleanUIStage() for code-only projects.

Start by reviewing the GraphicsCompositor.sdgfxcomp asset and related PR #1603, then compare the StrideCleanUI setup with the default new-project templates. Done means new projects include a UserInterface render stage using RenderGroup31, UI renders cleanly in the editor and game without post-processing, and existing projects remain unchanged.