fix(ci): increase browser test per-file timeout to 300s

The ChatView.browser.tsx file (~1900 lines, 20+ integration tests)
consistently times out at the previous 120s limit on CI runners.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Author: BunsDev

scripts/run-browser-tests.mjs

@@ -6,7 +6,7 @@ import { createRequire } from "node:module";
 import path from "node:path";
 import process from "node:process";
 
-const DEFAULT_TIMEOUT_MS = 120_000;
+const DEFAULT_TIMEOUT_MS = 300_000;
 const BROWSER_TEST_SUFFIX = ".browser.tsx";
 
 function listBrowserTests(rootDir) {