[FE-08] Build DocumentUpload component with file preview

[Alqku]

Closes #876

Adds DocumentUpload component with:

• Drag-and-drop file upload zone with visual feedback
• File type restriction (PDF, PNG, JPG)
• Maximum file size validation (10MB)
• File preview (image thumbnails for PNG/JPG, icon for PDF)
• Document type selector (BILL_OF_LADING, PROOF_OF_DELIVERY, INVOICE, INSURANCE_CERT, OTHER)
• Upload progress bar animation
• Error state display for invalid files

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