fix(build): retry transient sitemap endpoint fetches

The TypeScript helper refactor exposed a separate production risk: builds can fail when the sitemap-endpoints API returns a transient 5xx during Pagefind index generation. Move that fetch into a small helper with retry logic and add a focused prebuild test so this failure mode is caught without waiting on a full deploy.

Constraint: Must keep Pagefind index generation behavior the same when the endpoint is healthy
Rejected: Ignore the failure as external-only | transient 5xx responses can still block deploys and CI repeatedly
Confidence: high
Scope-risk: narrow
Reversibility: clean
Directive: When external build inputs can fail transiently, add a small retryable helper plus a direct test before relying on full deploy verification
Tested: pnpm exec vitest run test/prebuild/load-sitemap-endpoints.test.ts; pnpm run typecheck; pnpm run test-prebuild
Not-tested: Full production redeploy completion before push

scripts/build-pagefind-index.js

@@ -1,31 +1,12 @@
-import fs from 'fs-extra'
-import axios from 'axios'
 import 'dotenv/config.js'
 
 import {
-    sitemapEndpointsPath
-} from '~/helpers/pagefind/config.js'
+    loadSitemapEndpoints
+} from '~/helpers/pagefind/load-sitemap-endpoints'
 import {
     writePagefindIndex
 } from '~/helpers/pagefind/index.js'
 
-async function loadSitemapEndpoints () {
-    if ( await fs.pathExists( sitemapEndpointsPath ) ) {
-        return await fs.readJson( sitemapEndpointsPath )
-    }
-
-    if ( !process.env.PUBLIC_API_DOMAIN ) {
-        throw new Error(`Missing ${ sitemapEndpointsPath } and PUBLIC_API_DOMAIN is not set`)
-    }
-
-    const apiUrl = new URL( process.env.PUBLIC_API_DOMAIN )
-    apiUrl.pathname = sitemapEndpointsPath.replace(/^\.?\/?static\//, '/')
-
-    const response = await axios.get( apiUrl.toString() )
-
-    return response.data
-}
-
 ;(async () => {
     const sitemapEndpoints = await loadSitemapEndpoints()
     const {