Offer Generate with AI inside each media type tab, as a switch next to Upload

Problem/Motivation

Each media type with a generator adds its own "Generate … with AI" tab to the Media Library. On a site with Image, SVG Image and Video that makes 8 tabs instead of 5, and the AI path sits away from the upload it replaces. Editors think "I need an image", then choose how to add it.

Steps to reproduce

1. Open the Media Library from a field or the editor that allows Image, SVG Image and Video.
2. See three extra "Generate … with AI" tabs in the tab list.

Proposed resolution

• Add a third choice to "Where should the AI tabs appear?" (tab_position): Inside the tab of its media type. The tab list is core's, and inside Image, SVG Image and Video a small switch reads "Upload | Generate with AI New" ("Add" for Video).
• Each mode keeps its own URL (ai_media=1), so it works with the Media Library's AJAX and without new state.
• Keep "Right after the tab of their media type" and "After all the other tabs" for sites that want standalone tabs.
• Make the new choice the default for new installs.
• Style it with the admin theme's own variables, for Gin and Default Admin; labels never wrap.
• Editors without a provider see no switch; administrators see "Not set up" and the setup message.

AI-Generated: Yes

Remaining tasks

• ✅ File an issue
• ❌ Addition/Change/Update/Fix
• ❌ Testing to ensure no regression
• ❌ Automated unit/functional testing coverage
• ❌ Developer Documentation support
• ❌ User Guide Documentation support
• ❌ UX/UI designer responsibilities
• ❌ Accessibility and Readability
• ❌ Reviewed by a human
• ❌ Code review by maintainers
• ❌ Full testing and approval
• ❌ Credit contributors
• ❌ Review with the product owner
• ❌ Update Release Notes
• ❌ Release

User interface changes

• New setting choice; by default the AI option is a switch inside each media type's tab.

API changes

• None.

Data model changes

• tab_position accepts inside, the new default.

Release notes snippet

• Generate with AI can sit inside each media type's tab in the Media Library, as a switch next to Upload.