refactor(web): remove assigner panel React.FC

[lyzno1]

Summary

• type the assigner panel parameter directly instead of using React.FC
• import memo directly instead of retaining the React namespace
• leave the rendered tree and runtime behavior unchanged

Boundary

This PR is deliberately isolated from the semantic fix and CSS icon conversion. It changes only the component declaration and import shape.

Validation

• pnpm --dir web exec vp test run app/components/workflow/nodes/assigner/__tests__/panel.spec.tsx — 1 passed
• pnpm --dir web lint:a11y app/components/workflow/nodes/assigner/panel.tsx — passed
• focused lint — passed
• pnpm check — 0 errors, 2058 warnings
• git diff --check — passed

Visual regression review

The runtime output should be byte-for-byte equivalent at the component boundary. Any DOM, interaction, layout, or visual difference is a regression.

Stack

Depends on #40338. Final PR in stack #40340.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
⚠️ Please upload report for BASE (codex/refactor-assigner-add-icon@db93330). Learn more about missing BASE report.

Additional details and impacted files

@@                         Coverage Diff                         @@
##             codex/refactor-assigner-add-icon   #40339   +/-   ##
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  Coverage                                    ?   86.43%           
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  Files                                       ?     5107           
  Lines                                       ?   290741           
  Branches                                    ?    57924           
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  Hits                                        ?   251291           
  Misses                                      ?    34509           
  Partials                                    ?     4941           

Flag	Coverage Δ
dify-ui	93.49% <ø> (?)
web	86.11% <100.00%> (?)

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[lyzno1]

Closing during the accessibility stack audit. This layer only changes component typing or icon implementation, adds no user-visible accessibility contract, and carries independent visual/review risk. It can be reconsidered later as a separate cleanup, not as an a11y dependency.