fix(browser): surface detection details and docs

src/browser/routes/agent.shared.ts

@@ -63,7 +63,11 @@ export async function requirePwAi(
   jsonError(
     res,
     501,
-    `Playwright is not available in this gateway build; '${feature}' is unsupported.`,
+    [
+      `Playwright is not available in this gateway build; '${feature}' is unsupported.`,
+      "Install the full Playwright package (not playwright-core) and restart the gateway, or reinstall with browser support.",
+      "Docs: /tools/browser#playwright-requirement",
+    ].join("\n"),
   );
   return null;
 }