sync dev to ui

[qingqing-ux]

Summary

Sync the latest changes from dev into ui as a structural sync for the real frontend code.

Issue

Related to #3137

Background

This merged PR brought the real frontend code structure from dev into ui, so follow-up design and implementation work for #3137 can continue on top of the updated ui branch.

Conflict Resolution

ui/prototype exists on both branches:

• dev has placeholder files with not implemented content.
• ui has the full Vite/Vue prototype implementation.

This PR kept the existing ui implementation and applied the rest of the dev changes on top.

Verification

• Confirmed the PR was mergeable on GitHub before merge.
• Confirmed the local working tree was clean.

[gemini-code-assist]

Code Review

This pull request updates the SPX version to 2.0.1, increases the maximum file size for conversions, and significantly refines the AnimationVideoPreview component with improved seek handling and a more robust dragging implementation. The SPX documentation and API references are updated to reflect command overload changes and the support for top-level startup statements. Additionally, the Animation model now supports sound looping. Review feedback focused on replacing risky non-null assertions in the video preview component, correcting default value documentation for sound looping, and ensuring the loop property is correctly loaded from both current and legacy configuration blocks.

[gemini-code-assist]

The use of the non-null assertion operator (!) on videoDurationRef.value is risky. Although it is checked at the start of the drag, the duration could theoretically become null if the video source changes or the component state updates during the drag. It is safer to add an explicit null check.

    } else if (videoDurationRef.value != null) {
      cutEndRef.value = adjustEndTime(cutEndRef.value, videoDurationRef.value, true)
    }

[gemini-code-assist]

The comment indicates that onPlay defaults to true, but the implementation in Animation.load (line 191) and the corresponding tests (line 177 of animation.test.ts) default it to false. Please update the comment to reflect the actual behavior.

Suggested change

	/** Whether to loop the sound; for onStart defaults to false, for onPlay defaults to true */
	loop?: boolean
	/** Whether to loop the sound; defaults to false */
	loop?: boolean

[gemini-code-assist]

The loop field from the legacy onStart configuration is currently ignored during loading, even though soundName correctly falls back to it. The logic should be updated to check the loop property on whichever configuration block (onPlay or onStart) is being used.

    const actionConfig = onPlay ?? onStart
    const soundName = actionConfig?.play
    if (soundName != null) {
      const sound = sounds.find((s) => s.name === soundName)
      if (sound == null) console.warn(`Sound ${soundName} not found when creating animation ${name}`)
      else {
        soundId = sound.id
        soundLoop = actionConfig.loop ?? false
      }
    }