Fix/performance

[ptesei]

• improve performance using a strore
• no html changes for retro compatibility

Note

Medium Risk
Changes how tabsActive is derived from editor selection and when it updates, which can affect tab activation behavior (especially with nested tabs) despite being editor-only logic.

Overview
Refactors active-tab syncing so tabsActive is updated once per blockparty/tabs block via a new useSyncTabsActiveForTabsBlock hook, instead of rendering SyncTabsActive inside every nav/panel item.

The sync logic now infers the closest tab item from the current selection/ancestors, verifies ownership to avoid cross-updating nested tabs, and skips dispatches when tabsActive is already correct.

^{Reviewed by Cursor Bugbot for commit 4ebd332. Bugbot is set up for automated code reviews on this repo. Configure here.}