[Dashboard] Improve signal config enum and domain selection controls

[wilsonwu]

PLEASE FILL IN THE PR DESCRIPTION BELOW AND CONFIRM THE CHECKLIST ITEMS.

Closes N/A

Purpose

• Replace the Dashboard embedding signal Aggregation Method free-text input with a dropdown using the supported enum values.
• Replace the Domain signal MMLU Categories textarea with a richer category picker that supports:
  • selecting one or more preset MMLU domain categories
  • adding one or more custom categories
  • removing selected categories as tags
• These changes reduce invalid user input, make supported values easier to discover, and preserve extensibility for custom domain labels.
• Affected module(s): Dashboard

Test Plan

• Run make dashboard-check.
• Run focused frontend checks:
  • npm run lint
  • npm run type-check
  • npm run test:unit
• This validation is sufficient because the change is scoped to Dashboard config UI rendering and form serialization. It does not change router runtime behavior, backend handlers, or the config file schema.

Test Result

• make dashboard-check passed.
• Focused frontend checks passed:
  • npm run lint
  • npm run type-check
  • npm run test:unit
• Frontend unit tests passed: 11 test files, 40 tests.
• Existing npm audit warnings and Sass/Svelte deprecation warnings were printed during dashboard checks, but they are unrelated to this PR and did not fail validation.
• No follow-up blockers identified.

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Semantic Router PR Checklist

• PR title uses module-aligned prefixes such as [Router], [CLI], [Dashboard], [Operator], [Fleet-Sim], [Bindings], [Training], [E2E], [Docs], or [CI/Build]
• If the PR spans multiple modules, the title includes all relevant prefixes
• Commits in this PR are signed off with git commit -s
• The Purpose, Test Plan, and Test Result sections reflect the actual scope, commands, and blockers for this change

See CONTRIBUTING.md for the full contributor workflow and commit guidance.

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[github-actions]

👥 vLLM Semantic Team Notification

The following members have been identified for the changed files in this PR and have been automatically assigned:

📁 dashboard

Owners: @Xunzhuo, @JaredforReal, @haowu1234, @szedan-rh, @yehuditkerido, @henschwartz
Files changed:

• dashboard/frontend/src/pages/ConfigPageDomainCategoryPicker.module.css
• dashboard/frontend/src/pages/ConfigPageDomainCategoryPicker.tsx
• dashboard/frontend/src/pages/ConfigPageSignalsSection.tsx

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🎉 Thanks for your contributions!

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[github-actions]

✅ Supply Chain Security Report — All Clear

Scanner	Status	Findings
AST Codebase Scan (Py, Go, JS/TS, Rust)	✅	19 finding(s) — MEDIUM: 12 · LOW: 7
AST PR Diff Scan	✅	No issues detected
Regex Fallback Scan	✅	No issues detected

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Scanned at 2026-06-15T11:46:29.716Z · View full workflow logs

[wilsonwu]

The CI process encountered instability with the Docker image registry, reviewer who can help to trigger a retry, thank you.

[AayushSaini101]

thanks for the MR @wilsonwu can you share the screenshots of the improvements thanks 🙏

[wilsonwu]

thanks for the MR @wilsonwu can you share the screenshots of the improvements thanks 🙏

Yes, I've optimized the UI of Domain Signal, making it easy and quick to select multiple preset domains, and also allowing for custom domain selection.

Both the editing interface and the view interface are functioning normally.

[AayushSaini101]

LGTM thanks 🙏