D2: bound the navigation guard's tab reset (commit, 5 s)

Ubicloud run 3: a click to a link-local link reported the block, but the
reset's page.goto('about:blank') waited the full 30 s default navigation
timeout, so the command hung past the test deadline and the stale block
leaked into the next command. The reset now waits for commit only, with a
5 s bound.

browse/src/browser-manager.ts

@@ -2106,7 +2106,8 @@ export class BrowserManager {
         if (!reason || page.isClosed()) return;
         guard.blocked = reason;
         console.warn(`[browse] ${reason} (navigation from ${req.frame().url() || 'a new page'}; tab reset to about:blank)`);
-        await page.goto('about:blank').catch(() => {});
+        // Commit is enough to blank the tab; a bounded reset never holds the command for the full navigation timeout.
+        await page.goto('about:blank', { waitUntil: 'commit', timeout: 5_000 }).catch(() => {});
       }).finally(() => { guard.pending.delete(check); });
       guard.pending.add(check);
     });