fix(license): support SPDX identifier field in OAS v3.1.0 License Object (#1365)

* feat(i18n): make QualifierMessage strings translatable

Move qualifier-message rendering fully to the theme layer so that
Docusaurus i18n can translate the human-readable constraint strings:
- "characters" (minLength / maxLength)
- "non-empty" (minLength === 1)
- "Value must match regular expression" (pattern)

Architecture:
- `getQualifierMessage` is removed from the plugin and kept only in
  the theme (`docusaurus-theme-openapi-docs/src/markdown/schema.ts`),
  where `translate()` is available at render time.
- `SchemaItem` now computes `qualifierMessage` from its `schema` prop
  when the caller doesn't pass one explicitly, so all callers are
  simplified — no more `qualifierMessage={getQualifierMessage(schema)}`
  at every call site.
- Plugin `createSchema.ts` and `Schema/index.tsx` drop all
  `qualifierMessage` prop passes; the theme component handles it.
- `utils.ts` `create()` skips props with `undefined` values, cleaning
  up generated MDX.
- Dead code removed: `humanizeConstraints`, `humanizeNumberRange`, and
  related helpers were exported but unused.

Translation IDs added:
  theme.openapi.schemaItem.characters
  theme.openapi.schemaItem.nonEmpty
  theme.openapi.schemaItem.expression

Demo directory intentionally untouched (no locale config added).

Closes #1249. Credit: @dsuket

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

* fix(license): support SPDX identifier field in OAS v3.1.0 License Object

Adds rendering support for the `identifier` field introduced in OAS v3.1.0,
which is mutually exclusive with `url`. When present, links to the canonical
SPDX license page at https://spdx.org/licenses/<identifier>.html.

Closes #1319

* test(license): add demo test spec for SPDX identifier support

Adds licenseIdentifier.yaml to demo/examples/tests to verify that a spec
using license.identifier renders a clickable SPDX license link correctly.

Related to #1319

* test(license): add licenseUrl.yaml for regression check alongside identifier test

Related to #1319

* fix(types): add identifier field to LicenseObject

Required for createLicense.ts to compile after adding SPDX identifier support.

Closes #1319

---------

Co-authored-by: Claude Sonnet 4.6 <noreply@anthropic.com>

Author: sserrata

demo/examples/tests/licenseIdentifier.yaml

@@ -0,0 +1,29 @@
+openapi: 3.1.0
+info:
+  title: License Identifier Demo API
+  description: |
+    Demonstrates OAS v3.1.0 `license.identifier` support (SPDX expression).
+
+    Per the OAS v3.1.0 spec, `identifier` and `url` are mutually exclusive.
+    When `identifier` is present, a link to the canonical SPDX license page
+    should be rendered in the License section.
+  version: 1.0.0
+  license:
+    name: Apache 2.0
+    identifier: Apache-2.0
+tags:
+  - name: licenseIdentifier
+    description: License identifier tests
+paths:
+  /license-identifier:
+    get:
+      tags:
+        - licenseIdentifier
+      summary: License rendered via SPDX identifier
+      description: |
+        This endpoint exists to verify that a spec using `license.identifier`
+        (instead of `license.url`) correctly renders a clickable license link
+        pointing to `https://spdx.org/licenses/Apache-2.0.html`.
+      responses:
+        "204":
+          description: No content

demo/examples/tests/licenseUrl.yaml

@@ -0,0 +1,27 @@
+openapi: 3.1.0
+info:
+  title: License URL Demo API
+  description: |
+    Demonstrates `license.url` rendering (regression check).
+
+    Verifies that the existing `license.url` behavior is unaffected by the
+    addition of `license.identifier` support.
+  version: 1.0.0
+  license:
+    name: Apache 2.0
+    url: https://www.apache.org/licenses/LICENSE-2.0.html
+tags:
+  - name: licenseUrl
+    description: License url tests
+paths:
+  /license-url:
+    get:
+      tags:
+        - licenseUrl
+      summary: License rendered via URL
+      description: |
+        Verifies that a spec using `license.url` renders a clickable license
+        link pointing to the provided URL.
+      responses:
+        "204":
+          description: No content

packages/docusaurus-plugin-openapi-docs/src/markdown/createLicense.ts

@@ -10,7 +10,7 @@ import { LicenseObject } from "../openapi/types";
 
 export function createLicense(license: LicenseObject) {
   if (!license || !Object.keys(license).length) return "";
-  const { name, url } = license;
+  const { name, url, identifier } = license;
 
   return create("div", {
     style: {
@@ -29,6 +29,12 @@ export function createLicense(license: LicenseObject) {
           children: name ?? url,
         })
       ),
+      guard(identifier, () =>
+        create("a", {
+          href: `https://spdx.org/licenses/${identifier}.html`,
+          children: name ?? identifier,
+        })
+      ),
     ],
   });
 }

packages/docusaurus-plugin-openapi-docs/src/openapi/types.ts

@@ -65,6 +65,7 @@ export interface ContactObject {
 export interface LicenseObject {
   name: string;
   url?: string;
+  identifier?: string;
 }
 
 export interface ServerObject {