[Aymericr]

What does this PR do?

Adds an explicit host history Interface so the hosted collaborative editor can expose immediate undo/redo state and results without changing standalone Zundo behavior.

It also adds idempotent scene-history pause leases and migrates the fence/wall curve interactions that could release history twice during cancel plus effect cleanup. Command-palette history actions now follow the active history availability.

This is the public editor half of the hosted collaboration journal fix.

How to test

1. Run bun run check && bun run check-types && bun run build.
2. Run bun test packages/core/src packages/editor/src packages/nodes/src.
3. In standalone editor mode, verify undo/redo still use the local Zundo stacks; with a host delegate installed, verify commands and availability come from the host.

Screenshots / screen recording

Not applicable; this changes history behavior and ownership without a visual redesign.

Checklist

• Tested locally with bun dev
• Code style verified with bun check
• Relevant documentation updated where applicable
• This PR targets the main branch