fix(web-app-ai-quick-draft-creator): improve new file action icon and label

[LukasHirt]

Summary

• Changed the "New file" menu action icon from draft (a generic blank-document glyph indistinguishable from other file-type entries) to sparkling-2, matching the icon convention already used by every other AI extension in this repo (ai-folder-brief-sidebar, ai-data-insights-sidebar, ai-doc-summary, ai-folder-readme-generator, ai-multi-doc-synthesizer, ai-image-alt-text-sidebar, ai-smart-file-tagger-qa, ai-smart-collections-nav).
• Changed the menu label from "Draft from description" to "Generate a file with AI" so the entry clearly communicates it's an AI-powered feature, per the issue's own suggested wording.
• Updated the e2e test (tests/e2e/acceptance.spec.ts) and the package README to reference the new label so they stay in sync with the UI copy.

Before → After:

• icon: 'draft' → 'sparkling-2'
• label: "Draft from description" → "Generate a file with AI"

Closes #529

Test plan

• pnpm --filter web-app-ai-quick-draft-creator check:types passes
• pnpm --filter web-app-ai-quick-draft-creator lint passes
• pnpm --filter web-app-ai-quick-draft-creator test:unit passes (11/11)
• Verified sparkling-2 is the established AI-icon convention via grep across packages/web-app-ai-*/src/index.ts
• Verified sparkling-2-line.svg / sparkling-2-fill.svg exist in the design system icon set

[kw-security]

✅ Snyk checks have passed. No issues have been found so far.

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