fix(theme): scope inner CodeTabs defaultValue to current language's samples

The inner x-codeSamples CodeTabs was passing the global selectedSample
state as defaultValue for every outer language tab. When selectedSample
held an id from a different language (e.g. "Python-KeyPair Auth" while
rendering the C# tab), Docusaurus's <Tabs> validation threw:
"<Tabs> has a defaultValue 'Python-KeyPair Auth' but none of its
children has the corresponding value. Available values are: C#-0."

Guard the defaultValue so each language's inner tabs only adopt
selectedSample when the id belongs to that language's samples;
otherwise fall back to the language's first sample.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

Author: sserrata

packages/docusaurus-theme-openapi-docs/src/theme/ApiExplorer/CodeSnippets/index.tsx

@@ -296,7 +296,11 @@ function CodeSnippets({
                   }}
                   includeSample={true}
                   currentLanguage={lang}
-                  defaultValue={selectedSample}
+                  defaultValue={
+                    selectedSample && lang.samples.includes(selectedSample)
+                      ? selectedSample
+                      : lang.samples[0]
+                  }
                   languageSet={mergedLangs}
                   lazy
                 >