Add AnimationConflictMode enum with three modes:
- REPLACE (default): Complete existing animation and start new one
- QUEUE: Wait for existing animation to complete before starting
- ERROR: Raise RuntimeError if property is already being animated
Changes:
- AnimationManager now tracks property locks per (target, property) pair
- Animation.start() accepts optional conflict_mode parameter
- Queued animations start automatically when property becomes free
- Updated type stubs with ConflictMode type alias
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Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>
