Add accessibility coverage for PackageSizeIncreaseAnalysis

[coderabbitai]

Summary

Add automated Vitest accessibility coverage for PackageSizeIncreaseAnalysis and remove its temporary exclusion from the component-coverage guard.

The component currently depends on the worker-backed useAnalyzeCauseWorker composable, so the test must isolate the UI from real Web Worker and IndexedDB behaviour.

Required changes

• Add an accessibility/component test for app/components/Package/SizeIncreaseAnalysis.vue.
• Mock useAnalyzeCauseWorker (and the worker boundary if the established test setup requires it) with reactive, type-safe state and no-op actions.
• Cover the initial available state and assert that axe reports no accessibility violations.
• Remove the Package/SizeIncreaseAnalysis.vue TODO/entry from SKIPPED_COMPONENTS in test/unit/a11y-component-coverage.spec.ts.

Rationale

The current skip leaves the new package-size analysis UI outside the repository’s required component accessibility coverage. A deterministic mock prevents browser-worker and IndexedDB dependencies from making the test brittle.

Affected areas

• app/components/Package/SizeIncreaseAnalysis.vue
• app/composables/pkg-size/useAnalyzeCauseWorker.ts
• test/nuxt/a11y.spec.ts (or the established component-test location)
• test/unit/a11y-component-coverage.spec.ts

Acceptance criteria

• A Vitest test mounts PackageSizeIncreaseAnalysis with a mocked analysis composable.
• The test performs an axe accessibility assertion without starting a real worker.
• The temporary coverage skip and its TODO are removed.
• The relevant test suite passes.

Requested by @userquin.

Backlinks: #3077 and #3077 (comment)