ci(pages): [CI-02] validate staged artifacts and preserve legacy demo paths

scripts/prepare-pages.mjs

@@ -0,0 +1,10 @@
+import assert from 'node:assert/strict'
+import fs from 'node:fs'
+import process from 'node:process'
+import { preparePages } from './pages/prepare.ts'
+
+assert.equal(process.argv.length, 2, 'Use yarn prepare:pages without arguments')
+const result = await preparePages(process.cwd())
+if (process.env.GITHUB_OUTPUT)
+  fs.appendFileSync(process.env.GITHUB_OUTPUT, `site=${result.site}\n`)
+console.log(`Pages artifact validated: ${result.site}; ${Object.keys(result.report.files).length} files. No deployment was performed.`)