Fix FrameAccumulator to return initial frame on creation

[bengotow]

Summary

Updated FrameAccumulator.getFrames() to return the initial frame state when no changes have been recorded, rather than returning an empty array.

Key Changes

• Modified the test expectation in getFrames test case to verify that an initial frame is returned containing the actors passed to the constructor
• The initial frame now properly captures the starting state of all actors, ensuring the frame history always includes at least the initial state

Implementation Details

• When FrameAccumulator is instantiated with actors, calling getFrames() now returns an array with one frame containing those initial actors
• This ensures consumers of the API always have access to the initial state, which is important for proper animation/frame playback logic

https://claude.ai/code/session_01WxSXMrHTBGAQbs44SKjBQa