Add UPS Lag Diagnosis Report

[google-labs-jules]

Added UPS_LAG_REPORT-jules.md containing a detailed technical analysis of the UnifiedPlayerSheet performance issues.
The report identifies:

1. Recompositions: Caused by reading playerContentExpansionFraction.value directly in the composition scope (e.g., for zIndex) and using it in layout-affecting modifiers (height, padding).
2. Alpha Jitter: Caused by using updateTransition with a continuous float value, forcing constant animation restarts.

Proposals included:

• Replacing updateTransition with linear interpolation (lerp).
• Isolating state reads using derivedStateOf.
• Moving visual updates to graphicsLayer.

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PR created automatically by Jules for task 11551973758636712627 started by @theovilardo

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