feat: #3633456 Tag every AI Media request for Drupal AI Logging and observability

Issue: #3633456

AI Media calls already carried ai_media, ai_media_generator:<id> and the media type, but not the step, so AI Logging and AI Observability could not tell the media call from the "Ask AI" name, alt or title calls.

What changed

• AiMediaRequest::tags() adds ai_media:<generator> and ai_media_step:<step> (generate, name, alt or title). The existing tags stay, so moderation rules and filters on them keep working.
• The tags travel with the call; the AI module's provider proxy sets them with setTag() (a setTag() made before the call would be reset by the proxy).
• Docs: the tag table, and how to filter AI Logging and AI Observability by these tags. The Usage note on the Providers settings names them.

Tested

• Kernel AiMediaRequestTest::testTagsAndParentId checks the new tags on the image call and the alt call, as the provider reports them. Passes locally on Drupal 11.4 (7 tests).
• Dev site (Varbase 11, AI Logging 1.3.3): one SVG with OpenAI gpt-4.1-mini; the AI Logs entries carry chat, ai_media, ai_media:svg, ai_media_step:generate, ai_media_generator:svg, ai_media_media_type:svg_ai_gen.
• phpcs (Drupal, DrupalPractice) and phpstan level 0 clean; cspell clean on the changed files.

AI-Generated: Yes. Drafted and tested with Claude Code.

Checkpoints:

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

🤖 Generated with Claude Code