#3185 Docs: state the literal type/version catalog contract and the uncatalogued-model push warning in the extensions publishing reference

Follows swamp-club#2486.

content/manual/reference/extensions/publishing.md should:

• State that the registry catalog reads a model's type and version as string literals from a plain export const model = { ... } object. Models built by a shared factory and spread into the export must repeat both literals there, and the export must not carry a type annotation (use satisfies after the object instead). A model that does not meet this still installs and runs, but the registry does not list it, so it is missing from extension search --content-type models and extension info contentMetadata.models.
• List the new warning-level rule uncatalogued-model next to bare-specifiers in the push warnings section: it reports each model entry point the catalog would leave out and what could not be read (a non-plain export, a missing literal type, or a missing literal version). Like bare-specifiers it cannot be accepted. It appears in extension push (including --dry-run and --json) and extension quality, and changes no exit code.