fix: resolve race condition in anchor positioning for newly created anchors

[Antamansid]

Problem

When creating new endpoints on HTML layer (zoomed-in React rendering), a race condition occurred between React and Canvas rendering cycles:

• React components immediately subscribed to $anchorStates signal changes
• Canvas anchor initialization happened later via lifecycle hooks
• React tried to access anchor position before Canvas component was ready
• This caused crashes or incorrect positioning (anchors rendered at 0,0)

Solution

Added a readiness signal to synchronize React and Canvas rendering:

1. AnchorState: Added public $viewComponentReady signal
2. setViewComponent(): Sets the signal to true when Canvas anchor is initialized
3. useBlockAnchorPosition(): Waits for readiness before accessing anchor position

This ensures React re-renders automatically when the Canvas component becomes available, eliminating the race condition without breaking encapsulation.

[gravity-ui-bot]

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