perf(workspace): switching SQL tabs builds up to 8 ms in one frame #985

Summary

Switching SQL editor tabs builds up to 6.8–7.9 ms in one frame (real app, new_tab_and_switch), which does not fit the 144 Hz budget together with raster.

Scope

• Profile the switch frame (which subtrees rebuild: editor, results, toolbar).
• Keep inactive tabs' results and editor mounted but not rebuilt; rebuild only the tab strip and the swapped body.
• Target: < 4 ms build.