Generated schema pages do not show inherited fields from embedded structs

## Summary 🤖

When [work here ](https://github.com/gemaraproj/gemara/pull/478) is ready and merged, Gemara OpenAPI generator will represent embedded CUE definitions with OpenAPI composition:

```
ControlCatalog:
allOf:
- $ref: "#/components/schemas/Catalog"
properties:
controls: ...
```

This is valid and preserves the source model, but schema reference pages must resolve `allOf` to display inherited properties and required fields.

Without resolution, pages for schemas such as ControlCatalog, ThreatCatalog, GuidanceCatalog, and log types omit fields inherited from their base schemas.

The generator also uses `allOf` to attach a field description to a `$ref` property, as OpenAPI 3.0 forbids `$ref` siblings:

```
metadata:
description: metadata provides detailed data about this catalog
allOf:
- $ref: "#/components/schemas/Metadata"
```

## Acceptance criteria:
- Schema pages display properties inherited through local `allOf` $ref entries.
- Inherited required fields are shown as required.
- Properties declared directly on the derived schema override inherited properties with the same name.
- Multi-level allOf inheritance is resolved.
- Cyclic references do not cause infinite recursion or page-generation failure.
- A description-plus-allOf property wrapper remains represented as one property and retains its description.
- Add fixture coverage using a derived catalog schema and at least one described $ref field.

Start by locating the Go entry point that generates schema reference pages and the existing fixture or generator tests; the issue does not name specific files. Trace how local allOf $ref entries and wrapped described properties are represented, then add fixture coverage for derived catalogs and verify inherited fields, requiredness, overrides, multi-level inheritance, and cyclic references.

Written by the indexing model from the issue text.