Ready to Use YouTube Playables SDK for Unity WebG

[crudeGithub]

Summary

Integrates the YouTube Playables Web SDK wrapper into the project to support YouTube WebGL playable requirements.

Key Changes

• YouTube SDK Bridge: Added C# wrappers and JS plugins (.jslib) for game ready/lifecycle, cloud saves, scores, ads, audio sync, and pausing.
• Automatic WebGL Build Patching: Added an editor build postprocessor to automatically inject the YouTube SDK script and initialization hooks into the built index.html.
• Editor Fallbacks: Implemented fallback saving (via PlayerPrefs) and ad simulators to allow local development and testing.
• Documentation & Samples: Included step-by-step setup guides (INTEGRATION_GUIDE.md) and a sample script for integration references.

Verification

• Verify build output contains the YouTube script in index.html.
• Verify Editor testing falls back to PlayerPrefs and does not crash.