Add PDF accessibility upload blocking feature

Nicholas Steesrequested to merge
issue/pdf_services-3565944:3565944-block-form-saving-version2 into 1.0.x
  • Add 'bypass pdf accessibility checks' permission for role-based access control
  • Create pdf_accessibility_bypass table for storing justifications
  • Add 'block_failed_accessibility_on_new_upload' field-level configuration setting
  • Create PdfAccessibilityUploadValidator service for server-side validation
  • Enhance PdfFileWidget with accessibility validation and bypass UI
  • Add database migration hook to create bypass table
  • Add JavaScript library for accessibility validation form behavior
  • Detects NEW file uploads vs existing files to avoid blocking edits
  • Displays full accessibility report on validation failure
  • Allows bypass with justification for users with permission
  • Gracefully degrades if accessibility check not complete or API down

Closes #3565944

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