fix: isolate node selector keyboard events

[lyzno1]

Summary

• Add an opt-in keyboard event isolation mode to the workflow node selector popover.
• Enable it only for the Add Nodes entry opened from the workflow panel context menu.
• Cover the isolated keyboard path and AddBlock prop forwarding with focused tests.

Root Cause

When Add Nodes is opened from the workflow panel context menu, the Base UI context menu remains open behind the node selector. Its menu keyboard text navigation can consume printable English key events before the selector search can use them. The normal AddBlock entry is unaffected because there is no parent keyboard-managed menu overlay.

Validation

• pnpm -C web test app/components/workflow/block-selector/__tests__/main.spec.tsx app/components/workflow/operator/__tests__/add-block.spec.tsx app/components/workflow/__tests__/panel-contextmenu.spec.tsx
• git diff --check

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 85.28%. Comparing base (4cd8b8c) to head (e374314).
⚠️ Report is 2 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main   #37998   +/-   ##
=======================================
  Coverage   85.28%   85.28%           
=======================================
  Files        4938     4938           
  Lines      256081   256086    +5     
  Branches    48563    48566    +3     
=======================================
+ Hits       218398   218403    +5     
  Misses      33436    33436           
  Partials     4247     4247           

Flag	Coverage Δ
dify-ui	94.94% <ø> (ø)
web	84.77% <100.00%> (+<0.01%)	⬆️

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