fix(ai-gateway): Align AI landing pages with 0.0.47 API schema changes

[tomek-labuk]

Description

Recap of changes:

• entities.yaml: AI Provider card → AI Model Provider; "Model entity" CTA → "AI Model entity"; added AI Identity Provider card to Security section
• ai-gateway.yaml: "AI Providers" → "AI Model Providers" throughout; added AI Model Providers + AI Identity Providers to entity list; fixed commented-out card URL
• ai-providers.yaml: link text + URL → AI Model Provider

Preview Links

Checklist

• Tested how-to docs. If not, note why here.
• All pages contain metadata.
• Any new docs link to existing docs.
• All autogenerated instructions render correctly (API, decK, Konnect, Kong Manager).
• Style guide (capitalized gateway entities, placeholder URLs) implemented correctly.
• Every page has a description entry in frontmatter.
• Add new pages to the product documentation index (if applicable).

[Copilot]

Copilot reviewed 3 out of 3 changed files in this pull request and generated no comments.

[cloudjumpercat]

One nitpick!

[cloudjumpercat]

Suggested change

	description: Register upstream LLM providers with authentication and configuration. Reusable across models.
	description: Register upstream LLM providers with authentication and configuration. Reusable across AI Models.