feat: add frontend support for dual-track processing
- Add ProcessingTrack, ProcessingMetadata types to apiV2.ts
- Add analyzeDocument, getProcessingMetadata, downloadUnified API methods
- Update startTask to support ProcessingOptions
- Update TaskDetailPage with:
- Processing track badge and description display
- Enhanced stats grid (pages, text regions, tables, images, confidence)
- UnifiedDocument download option
- Translation UI preparation (disabled, awaiting backend)
- Mark Section 7 Frontend Updates as completed in tasks.md
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Co-Authored-By: Claude <noreply@anthropic.com>
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