Summary

Improve builder UX with preloaded element library, fix canvas outline blinking,
and resolve URL/layer selection issues when switching between panels.

Changes

• Preload element library elements and images for instant display
• Fix canvas outlines from sometimes blinking during selection
• Prevent unneeded multiple URL updates when selecting a page
• Fix URL sync and layer selection when switching between Layers and Pages tabs

Test plan

• Open element library — elements and images should load instantly
• Select the already selected layer on canvas or layer tree — outlines should not blink
• Switch between pages — URL should update once, not multiple times
• Switch between Layers and Pages tabs — selected layer should persist correctly