fix(web): name assigner add operation

[lyzno1]

Summary

• give the existing assigner Add action its localized accessible name
• hide the glyph from the accessibility tree
• replace the positional test query with role and name

Review boundary

Form submission, validation, fields, event handling, elements, classes, and layout are unchanged.

Verification

• owner suite: 1/1 passed
• standalone a11y lint: 0 diagnostics
• full static check: 0 errors
• diff check: passed

Visual regression and dependency

Production changes are ARIA-only, so normal pixels remain identical. This is an independent root layer; former icon and typing cleanup children are closed.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 86.43%. Comparing base (7522ae1) to head (48aae30).
⚠️ Report is 14 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #40337      +/-   ##
==========================================
- Coverage   86.47%   86.43%   -0.05%     
==========================================
  Files        5264     5107     -157     
  Lines      294867   290741    -4126     
  Branches    59029    57924    -1105     
==========================================
- Hits       254976   251290    -3686     
+ Misses      34950    34510     -440     
  Partials     4941     4941              

Flag	Coverage Δ
cli	?
dify-ui	93.49% <ø> (ø)
web	86.11% <100.00%> (+<0.01%)	⬆️

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