refactor(web): migrate workflow panel context menu primitive

[lyzno1]

Summary

• Migrate workflow panel context menu to @langgenius/dify-ui/context-menu primitives
• Store pane menu viewport coordinates directly for virtual anchor positioning
• Update workflow menu tests to render real primitives and AddBlock

Tests

• pnpm -C web test app/components/workflow/__tests__/panel-contextmenu.spec.tsx app/components/workflow/hooks/__tests__/use-panel-interactions.spec.ts app/components/workflow/store/workflow/__tests__/panel-slice.spec.ts app/components/workflow/store/__tests__/workflow-store.spec.ts app/components/workflow/hooks/__tests__/use-selection-interactions.spec.ts
• pnpm -C web exec eslint app/components/workflow/panel-contextmenu.tsx app/components/workflow/hooks/use-panel-interactions.ts app/components/workflow/store/workflow/panel-slice.ts app/components/workflow/__tests__/panel-contextmenu.spec.tsx app/components/workflow/hooks/__tests__/use-panel-interactions.spec.ts app/components/workflow/hooks/__tests__/use-selection-interactions.spec.ts app/components/workflow/store/workflow/__tests__/panel-slice.spec.ts app/components/workflow/store/__tests__/workflow-store.spec.ts
• pnpm -C web type-check

[codecov]

Codecov Report

❌ Patch coverage is 79.06977% with 9 lines in your changes missing coverage. Please review.
✅ Project coverage is 85.66%. Comparing base (8f3e42e) to head (9d3b921).
⚠️ Report is 2 commits behind head on main.

Files with missing lines	Patch %	Lines
web/app/components/workflow/panel-contextmenu.tsx	75.67%	9 Missing ⚠️

Additional details and impacted files

@@           Coverage Diff           @@
##             main   #35787   +/-   ##
=======================================
  Coverage   85.66%   85.66%           
=======================================
  Files        4461     4461           
  Lines      209051   209059    +8     
  Branches    39074    39080    +6     
=======================================
+ Hits       179084   179092    +8     
  Misses      26803    26803           
  Partials     3164     3164           

Flag	Coverage Δ
dify-ui	93.01% <ø> (ø)
web	86.43% <79.06%> (+<0.01%)	⬆️

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