fix(web): name the embedded chat settings trigger

[lyzno1]

Summary

• Give the embedded chat settings trigger the same translated accessible name shown in its panel heading.
• Mark the CSS chat-settings icon as decorative.
• Exercise the trigger through its public button role and accessible name instead of relying on data-testid.

Behavior contract

• Assistive technology exposes the icon-only trigger as the chat settings action.
• Pointer activation still opens and closes the existing popover.
• The existing test ID remains available; this PR changes the test contract without treating test IDs as accessibility defects.

Visual regression review

This is an ARIA-only change. No element tag, class, style, text node, node order, popover geometry, or interaction state changed, so no visual delta is expected.

Validation

• pnpm exec vp check app/components/base/chat/embedded-chatbot/inputs-form/view-form-dropdown.tsx app/components/base/chat/embedded-chatbot/inputs-form/__tests__/view-form-dropdown.spec.tsx
• node scripts/lint-a11y.mjs app/components/base/chat/embedded-chatbot/inputs-form/view-form-dropdown.tsx
• pnpm exec vp test run app/components/base/chat/embedded-chatbot/inputs-form/__tests__/view-form-dropdown.spec.tsx (1/1)
• pnpm check (0 errors; 2059 existing warnings)

From Codex

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 86.41%. Comparing base (e036075) to head (9b2ef69).
⚠️ Report is 1 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main   #40250   +/-   ##
=======================================
  Coverage   86.41%   86.41%           
=======================================
  Files        5107     5107           
  Lines      290731   290750   +19     
  Branches    57917    57923    +6     
=======================================
+ Hits       251245   251265   +20     
+ Misses      34545    34544    -1     
  Partials     4941     4941           

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

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