feat(spec-dashboard): support explicit emitter coverage groups

[Timothee Guerin (timotheeguerin)]

The coverage overview gives data-plane and management-plane implementations separate cards even when they represent the same language. Grouping implicitly by display name would mix presentation with coverage identity.

Add explicit groups, with scenario-level union coverage and compact per-emitter percentages underneath:

groupEmitters: [
  {
    name: "C#",
    emitters: [
      "@azure-typespec/http-client-csharp",
      "@azure-typespec/http-client-csharp-mgmt",
    ],
  },
]

A scenario counts once per table and is covered if any member covers it. Grouping leaves table columns, report loading, and display names independent; ungrouped emitters retain their own cards.

Alternative to #11709 for the overview grouping in #11699. The Azure dashboard will need to opt into groupEmitters separately.

[github-actions]

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[azure-sdk-automation]

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[Copilot]

🟡 Changes recommended

The new public feature lacks the required @typespec/spec-dashboard feature changeset.

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Pull request overview

Adds explicit emitter grouping to Spec Dashboard coverage overviews, enabling union coverage across related emitters while preserving individual metrics.

Changes:

• Adds the public groupEmitters configuration.
• Computes scenario-level union coverage and per-emitter percentages.
• Adds comprehensive tests, styling, and documentation.

File summaries

File	Description
packages/spec-dashboard/src/apis.ts	Defines emitter-group configuration.
packages/spec-dashboard/src/index.ts	Exports EmitterGroup.
packages/spec-dashboard/src/components/dashboard.tsx	Passes groups to the overview.
packages/spec-dashboard/src/components/dashboard-az-storage.tsx	Supports groups in storage-backed dashboards.
packages/spec-dashboard/src/components/coverage-overview.tsx	Implements grouped union coverage cards.
packages/spec-dashboard/src/components/coverage-overview.test.tsx	Tests grouping and coverage calculations.
packages/spec-dashboard/src/components/coverage-overview.module.css	Styles grouped emitter details.
packages/spec-dashboard/src/utils/coverage-utils.ts	Shares completed-status detection.
packages/spec-dashboard/README.md	Documents grouping behavior and usage.
cspell.yaml	Adds the CSS term to spelling configuration.

Review details

• Files reviewed: 10/10 changed files
• Comments generated: 1
• Review effort level: Balanced

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