Creates a new user-generated widget with type-specific content structure.

Content format by widget type:

• RICH_TEXT: {"html": "HTML content"}
• AI_GENERATED_TEXT: {} (empty object - content is generated by calling the AI generation endpoint after widget creation)
• MEDIA_CONTENT: {"type": "YOUTUBE_VIDEO|LINK|FILE_UPLOAD|GOOGLE_WORKSPACE|PDF_UPLOAD", "url": "...", "fileId": "...", "title": "..."}
• USER_PDF: {"fileId": "uploaded-file-uuid"}

Media content types:

• YOUTUBE_VIDEO: YouTube video URLs
• LINK: Generic web links
• FILE_UPLOAD: References uploaded files via fileId
• GOOGLE_WORKSPACE: Google Docs/Sheets/Slides URLs
• PDF_UPLOAD: References uploaded PDF files via fileId

AI Generated content structure after generation:

• type: "AI_GENERATED_TEXT"
• aiContentId: UUID of the generated content record
• displayContent: The actual generated text content