Potential fix for pull request finding

Co-authored-by: Copilot Autofix powered by AI <175728472+Copilot@users.noreply.github.com>

Author: igalklebanov

site/scripts/verify-proof-links.mjs

@@ -65,7 +65,8 @@ for (const entry of entries) {
     console.log(`ok   ${entry.name} @ ${sha.slice(0, 7)}`)
   } catch (error) {
     failures++
-    console.warn(`warn ${entry.name}: ${error.message} — keeping existing permalink`)
+    const message = error instanceof Error ? error.message : String(error)
+    console.warn(`warn ${entry.name}: ${message} — keeping existing permalink`)
   }
 }