fix(ui): preserve tree drag and scroll across spaces

[antonreshetov]

Summary

Virtual tree dragging could lose its source before the drop handler ran, and HTTP data refreshes could scroll back to the selected entry. Keep the drag source mounted until dragend and reveal the active row only on navigation or initial mounting, after its data and expanded ancestors are available.

Enable the same virtual tree behavior for Code and Notes folders. Replace DOM-only folder scrolling with shared active-row reveal and connect new-folder rename requests to the virtual tree editor. Preserve selection and scroll across renames, moves and background refreshes.

This PR contains only tree changes on top of the optimizations already merged into main.

Validation

• 43 scoped tests passed across 9 files, including numeric folder navigation, nested folder expansion/reparenting, drag-source retention and scroll preservation.
• Scoped ESLint and commit hooks passed.
• Production Vite build passed (existing chunk-size warnings).
• HTTP dragging was previously confirmed manually by the user; HTTP rename scroll preservation was checked in an isolated app. Full native drag gestures in the newly virtualized Code and Notes trees have not been manually verified.