TINYDOC-3651: Correct and update the TinyMCE AI documentation for existing features.

[kemister85]

Ticket: TINYDOC-3651

Site: Staging branch

Changes:

• Corrects published TinyMCE AI pages: the streaming code sample, Translate identifiers, JWT error messages and token checks, and on-premises API endpoint paths.
• Documents tinymceai_service_url (including the Tiny Cloud URL) and the permissions each feature needs.
• Replaces facts repeated across pages with links to the API reference, and applies sentence-case headings and style fixes.

Main pages changed:

• Plugin options
  • Adds tinymceai_service_url, corrects the defaults and examples for the token provider, default model, welcome message and tool status options, and adds a section on detecting content written by the plugin.
• Chat
  • Adds the Chat controls, Current document and selection, and the API message flow, and matches button labels to the plugin (Apply all, Skip all, View details).
• Models
  • Renames Auto to Agent (agent-1), corrects the models endpoint to /v1/models/1, and documents translated descriptions, model dates and the enabled/allowed capability fields.
• Permissions
  • Corrects the conversation and review permission scopes, and adds an example token for all plugin features.
• API overview
  • Adds Versioning, Pagination, Error responses and Rate limit errors sections.
• On-premises troubleshooting
  • Adds startup errors (database privileges and TLS, migrations, provider configuration, EKS Auto Mode), a log reference and request tracing.

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Pre-checks:

• Branch is correctly prefixed

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Review:

• Documentation Team Lead has reviewed.