PDF document upload can silently fail or show generic error

[AnthonyRonning]

Problem

PDF document upload can appear to do nothing after a user selects a file, while image upload continues to work.

The current chat document upload path has a couple of UX/failure cases that can look like the document never attached:

• UnifiedChat.tsx checks file extensions case-sensitively, e.g. file.name.endsWith(".pdf"). Files named .PDF can pass the picker but miss all document-processing branches.
• If PDF extraction returns no usable text, the UI does not attach the document and may only show a generic Failed to process document message, depending on where the failure occurs.
• Support docs say PDFs must be text-based and under 10MB, but the app does not clearly surface that distinction to the user at selection time.

Suggested investigation/fix

• Normalize selected document filenames before extension checks (toLowerCase() or MIME/type-based handling).
• Add an explicit unsupported-document branch so valid-looking picker selections cannot no-op.
• Surface a more specific error when PDF text extraction fails or returns empty text, especially for scanned/image-only PDFs.
• Confirm behavior on current macOS desktop, iOS, and Android builds with:
  • lowercase .pdf
  • uppercase .PDF
  • text-based PDF under 10MB
  • scanned/image-only PDF under 10MB
  • PDF over 10MB

Relevant code

• frontend/src/components/UnifiedChat.tsx: handleDocumentUpload
• frontend/src-tauri/src/pdf_extractor.rs: extract_document_content
• docs/support-faq.md: file upload support guidance