feat(compositor): add text support with customizable properties

[3IMAD69]

screenrecording-2026-02-10_19-42-23.mp4

This pull request adds support for text layers to the VideoEditorPlayground component and documents the new text source API for the compositor. Users can now add, edit, and style text clips directly in the video editor interface, and the API documentation has been updated to reflect the new capabilities for working with text sources.

Video Editor Playground Enhancements:

• Added a "+ Add Text" button to allow users to insert text clips into the timeline (VideoEditorPlayground.vue).
• Implemented a dedicated text track in the timeline UI, with visual styling for text clips (VideoEditorPlayground.vue). [1] [2]
• Enabled editing of text properties (content, font, size, weight, color, alignment, shadow, stroke, background, etc.) in the inspector panel when a text clip is selected (VideoEditorPlayground.vue). [1] [2]
• Updated the composition logic to render text clips as layers on top of video/image layers (VideoEditorPlayground.vue). [1] [2]
• Added logic to create and update text sources using the compositor's new API, and to store text-specific properties in the clip data (VideoEditorPlayground.vue).

API and Documentation Updates:

• Documented the new loadText method, CompositorTextSource interface, and text source options in the compositor API reference (compositor.md). [1] [2]
• Added usage examples for creating and updating text sources in the compositor guide (compositor.md, guide/compositor.md).

Other Improvements:

• Adjusted track assignment logic to account for text clips, ensuring video/image tracks are not affected by text layers (VideoEditorPlayground.vue). [1] [2]
• Increased the timeline height and improved inspector panel scrolling for better usability with additional controls (VideoEditorPlayground.vue). [1] [2] [3]
• Updated type imports to include CompositorTextSource in preparation for worker support (compositor-worker.ts).