perf(ci): build only en locale in docs-site-checks

The Docusaurus build step (198s) is 79% of the docs-site-checks job
wall time and is the CI critical path. The site has two locales (en +
zh-Hans, ~700 pages total); building only the default locale in PR
checks halves the build time.

Follows the same pattern Docusaurus uses internally: a build:fast
script that runs `docusaurus build --locale en` for CI/preview builds,
while the full bilingual build runs only in deploy-site.yml for
production deploys.

deploy-site.yml is unchanged — it still runs `npm run build` (all
locales) on push-to-main and release.

.github/workflows/docs-site-checks.yml

@@ -49,5 +49,8 @@ jobs:
         working-directory: website
 
       - name: Build Docusaurus
-        run: npm run build
+        # Build only the default (en) locale in CI — the full bilingual
+        # build runs in deploy-site.yml on push-to-main / release.
+        # Same pattern Docusaurus uses internally (build:fast --locale en).
+        run: npm run build:fast
         working-directory: website

website/package.json

@@ -8,6 +8,7 @@
     "start": "docusaurus start",
     "prebuild": "node scripts/prebuild.mjs",
     "build": "docusaurus build",
+    "build:fast": "docusaurus build --locale en",
     "swizzle": "docusaurus swizzle",
     "deploy": "docusaurus deploy",
     "clear": "docusaurus clear",