docs: add usage example peer review template

[jankiluitel]

Summary

This PR adds a new Usage Examples tab to the SplashKit Peer Review documentation.

The new checklist is designed to make usage-example reviews more consistent and efficient by giving reviewers a standard set of checks to follow.

What was added
Required file checks for C++, Python, C# OOP, C# Top-Level, GIF and .txt
API focus and SplashKit function checks
Cross-language consistency checks
Code quality and testing checks
GIF and description checks
Repository cleanliness checks
Final approval readiness checklist

Motivation

This was created after identifying that usage-example reviews could benefit from a more consistent review process. The checklist was initially shared with the SplashKit team and, following leadership feedback, was expanded into the project documentation so it can be reused by current and future contributors.

Testing
Tested locally using the Astro development server
Confirmed the Peer Review page renders successfully
Confirmed the new Usage Examples tab displays correctly
Ran formatting/build checks before committing

Evidence

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[Osaid2993]

The Usage Examples review checklist is well structured and should help make reviews more consistent across the team. Nice addition.

[Rhinoatron]

Thanks for adding this. The checklist is indeed clear, useful, and covers the main things reviewers should be checking for usage example PRs, including required files, API focus, cross-language consistency, testing, output evidence, and repository cleanliness. I understand the placement in the peer review documentation is intentional, and that makes sense given this is a reviewer checklist. One small note: the checklist refers specifically to a GIF, but the current usage example template also allows an image or other relevant demo file. This does not block approval from me, but it may be worth broadening that wording. Approved.