fix(browser): remove catch-block originalJson reference (block-scoped to try)

originalJson is const inside the try block and not accessible from the
catch block (tsgo correctly flags this, tsc was lenient). The inner
try/catch around params.run() already restores res.json before
re-throwing, so the outer catch doesn't need the restore.

Fixes tsgo TS2304 in CI.

src/browser/routes/agent.shared.ts

@@ -191,10 +191,6 @@ export async function withRouteTabContext<T>(
 
     return result;
   } catch (err) {
-    // Ensure res.json is always restored for error handling.
-    if (params.res.json !== originalJson) {
-      params.res.json = originalJson;
-    }
     handleRouteError(params.ctx, params.res, err);
     return undefined;
   }