Filter non-actionable "frame window is not ready" errors from Sentry (#8420)

The "Error: frame window is not ready" is thrown by third-party scripts
or browser internals when accessing iframe.contentWindow before the
frame has finished loading. The error string does not exist in the
source code or any dependency, confirming it originates from external
code. These errors are not actionable and create noise in Sentry.

Closes #8384

Co-authored-by: Claude Opus 4.6 <noreply@anthropic.com>

Author: iHiD

app/javascript/utils/react-bootloader.tsx

@@ -61,6 +61,13 @@ if (process.env.SENTRY_DSN) {
       )
       if (isInvalidOriginError) return null
 
+      // Drop non-actionable iframe readiness errors (third-party scripts or browser internals
+      // accessing iframe.contentWindow before the frame is ready)
+      const isFrameNotReadyError = event.exception?.values?.some((ex) =>
+        ex.value?.includes('frame window is not ready')
+      )
+      if (isFrameNotReadyError) return null
+
       const tag = document.querySelector<HTMLMetaElement>(
         'meta[name="user-id"]'
       )