fix(banner): use "Sign in" as the migration banner CTA label (RQ-5181)

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

Author: vsanse

app/src/componentsV2/AppNotificationBanner/hooks/useBannerAction.ts

@@ -75,7 +75,7 @@ export const useBannerAction = (
         },
       },
       [BANNER_ACTIONS.MERGE_BSTACK_ACCOUNT]: {
-        label: "Link BrowserStack account",
+        label: "Sign in",
         type: "primary",
         onClick: () => {
           // Brings a web user back to the page they started from. LoginHandler reads and clears