Darken toolbar while entity/asset picker is active

[kpal81xd]

Summary

• toolbar stays visually active while entity and asset pickers are open
• this creates inconsistent focus compared to the picker mode emphasis
• add picker-mode toolbar darkening/inactive treatment for both picker flows

Details

• PR [FIX] Align entity picker hierarchy visibility styling #1898 intentionally addresses hierarchy tree/visibility bar darkening only
• this follow-up tracks toolbar visual state updates in picker mode without changing selection behavior
• target pickers: picker:entity and picker:asset