fix(docs): make the Starlight build pass

## Changes
- Bump @astrojs/starlight to ^0.32.0 so starlight-openapi 0.13's plugin
  contract (top-level setup hook) is supported
- Replace the no-arg docsLoader call with Astro's glob loader pointing
  at ../api-content so prose stays outside the Astro project tree
- Rename introduction.md → index.md and update the sidebar slug so the
  /docs/ root resolves instead of returning 404
- Commit package-lock.json so Vercel installs deterministically

## Verification
- npm run build produces 96 pages (7 narrative + 88 OpenAPI operations + 1
  releases timeline)
- /docs/, /docs/releases/, /docs/api-reference/operations/authlogin/ and
  every other route return 200 locally
- 14 release cards render with the brand-green "Latest" badge on v3.7.1

docs/api/package.json

@@ -12,7 +12,7 @@
     "astro": "astro"
   },
   "dependencies": {
-    "@astrojs/starlight": "^0.30.0",
+    "@astrojs/starlight": "^0.32.0",
     "astro": "^5.0.0",
     "sharp": "^0.33.5",
     "starlight-openapi": "^0.13.0"