feat: Add file upload component to client

[ayushpahwa]

What

Add a file upload UI component for uploading health reports (PDFs).

Details

• File input with drag-and-drop support
• PDF file type restriction
• File size validation
• Upload progress indicator
• Preview/confirmation before upload

Implementation Notes

• Use native <input type="file"> or library like react-dropzone
• Accept: .pdf files only (initially)
• Max size: TBD (e.g., 10MB)
• Send to server endpoint (see #TBD)

Suggested Component

interface FileUploadProps {
  onUpload: (file: File) => Promise<void>
  accept?: string
  maxSize?: number
}

Acceptance Criteria

• File upload component created
• Drag-and-drop works
• PDF-only restriction
• File size validation with error message
• Loading state during upload
• Success/error feedback