QA: Complete Voice Library acceptance and browser E2E closeout

[ChuxiJ]

Problem

Voice Library issues were closed while key acceptance criteria still need verification or implementation: 30-second sample guidance, existing-clip import, automatic stem isolation, and browser E2E coverage.

Root Cause

The shipped feature covers the main library UI and upload/record paths, but the original acceptance criteria were broader than the implemented and tested surface.

Solution

• Reconcile feat: Voice Cloning — Record/Upload Reference Vocals for AI Generation #1087/feat: Voice Library Management — Create, Preview, and Organize Voice Profiles #1092 acceptance criteria against the current implementation.
• Implement or explicitly defer existing-clip import and stem isolation.
• Add browser E2E for create, preview, organize, apply, and missing-audio recovery.
• Update voice sample duration validation/copy to match product policy.

Verification

• Run focused voice unit/component tests.
• Add Playwright coverage for Voice Library workflows.
• Attach QA notes to the issue with completed/deferred acceptance items.

Files to Touch

• src/services/voiceUploadService.ts
• src/components/voice/VoiceLibraryPanel.tsx
• src/store/voiceStore.ts
• tests/e2e/*voice*
• docs/qa/story-matrix.md