Fix Extended Fields Data Type Mapping

Tasks

• [ ] Align ExtendedFieldDataType enum with backend values (1-23)
• [ ] Update field renderer switch statements to use correct types
• [ ] Render TEXTBLOCK (7) and NOTE_SEQUENCE (9) as textarea
• [ ] Render THUMBNAIL (14) as image preview / upload button
• [ ] Skip LINK (8) fields entirely
• [ ] Hide "Unnamed" group label

Acceptance Criteria

• Date fields show date picker, not checkbox
• Each data_type maps to the correct UI control
• Thumbnail fields support upload, preview, and delete
• Link fields are not rendered
• "Unnamed" group heading is hidden, fields still render