File Converter Web App Builder for React

## Role

You are a senior full-stack engineer specializing in file processing systems. You build production-grade conversion pipelines that handle edge cases, corrupted files, and large file sizes with robust error recovery and optimal memory management.

## Task

Build a universal file converter web application with client-side processing that supports:

- **Documents**: PDF ↔ DOCX ↔ TXT ↔ MD ↔ HTML
- **Images**: PNG ↔ JPG ↔ WEBP ↔ SVG ↔ GIF
- **Spreadsheets**: XLSX ↔ CSV ↔ JSON
- **Media**: MP4 ↔ WEBM ↔ GIF

Create a clean, minimal interface inspired by Squoosh.app and Linear.app using React with TypeScript and shadcn/ui components.

## Context

The application must handle real-world enterprise scenarios: large files that exceed memory limits, corrupted data that crashes parsers, and sensitive documents that cannot be uploaded to servers. All processing must occur client-side using browser APIs for complete data privacy.

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## Technical Requirements

**Architecture**
- Modular converter classes for each file type with format validation
- Streaming support for files exceeding memory limits
- TypeScript interfaces for type safety
- Browser APIs only (no server uploads)

**User Experience**
- Batch processing with progress tracking
- Quality settings and metadata preservation options
- Keyboard shortcuts and preference persistence
- Dark mode support
- Mobile-responsive with touch-friendly controls

**Accessibility**
- WCAG 2.1 AA compliance
- Screen reader support with ARIA labels
- Full keyboard navigation
- Focus management and skip links

**Reliability**
- Comprehensive error handling for corrupted files
- Graceful degradation when formats are unsupported
- Memory management strategies (chunking, workers, cleanup)
- Clear user feedback for all operations

## Output

Provide production-ready code organized as:

1. **Interface Design** – Component structure, user flow, and interaction patterns
2. **Technical Architecture** – React components, TypeScript interfaces, library integrations, and state management
3. **Conversion Engine** – Modular converter classes with validation, transformation logic, and error handling
4. **Performance Optimization** – Streaming implementation, memory management, and file size handling
5. **UX Features** – Batch processing, progress tracking, keyboard shortcuts, and settings persistence
6. **Accessibility Implementation** – ARIA attributes, keyboard navigation, screen reader announcements
7. **Error Handling** – Recovery strategies for corrupted files, validation failures, and browser limitations
8. **Implementation Guide** – Development roadmap, testing strategy, and deployment considerations

Include specific library recommendations (e.g., pdf-lib, mammoth, papaparse, ffmpeg.wasm) with integration examples.