Problem

When a user/author is deleted in Joomla, their articles retain the original `created_by` ID which becomes orphaned (or 0). Opening such an article in the admin shows an empty/invalid author field. Saving the article preserves the broken state.

Solution

• ArticleModel.php — In `save()`, before delegating to `parent::save()`, validate `created_by`: if it is 0/empty or refers to a deleted user (DB check), auto-assign the current logged-in user's ID.
• Content.php — In `store()`, change the existing-article fallback for empty `created_by` from `0` to `$user->id` as a safety net for CLI/batch code that bypasses the model.

Testing Instructions

1. Delete a Joomla user who authored articles.
2. Open one of their orphaned articles in the admin editor — author field shows empty/invalid.
3. Save → verify `created_by` is now the current admin's ID (check article Info tab or DB).
4. Verify saving a normal article with a valid author leaves `created_by` unchanged.

Automated Cypress spec

```bash
npm run cypress:run -- --spec "tests/System/integration/administrator/components/com_content/ArticleOrphanedAuthor.cy.js"
```

Environment

• PHP: 8.3+
• Database: MySQL/MariaDB/PostgreSQL
• Branch: 6.2-dev

Fixes #47995