Summary of Changes

• Added contact field integration into Schema.org forms (Article, BlogPosting, Book, etc.) using Joomla’s Form API.
• Injected modal_contact selector into relevant role subforms (e.g. author, illustrator) so users can link Joomla Contacts directly.
• Extended the System Schemaorg plugin to enrich schema.org output with contact information, ensuring consistent JSON-LD data.

Testing Instructions

1. Go to the backend and edit or create an Article (or BlogPosting, Book, etc.).
2. In the Schema.org tab, choose a schema type (e.g. Article).
3. Inside the author (or illustrator) subform, a Select Contact field is now visible.
4. Save the item and check the frontend source → the JSON-LD output should now include enriched author/illustrator data from the contact.

Actual result BEFORE applying this Pull Request

• No direct way to link Joomla Contacts with Schema.org roles.
• Author/illustrator data had to be manually entered.
• No placeholder hints were shown to users.

Expected result AFTER applying this Pull Request

• Schema.org forms allow selecting Joomla Contacts.
• Saved schema.org data auto-fills from the chosen contact.
• JSON-LD output is more accurate and consistent without extra manual input.