Store a request/response capture for non-200 responses so failed
requests can be inspected in the activity log's Capture dialog, matching
the existing behavior for successful requests.
- extract storeCapture/decodeResponseBody helpers to share capture logic
between the success and non-200 paths
- record non-200 bodies (decompressed) so error details are viewable
- the activity UI already gates the View button on has_capture, so it
now appears for failed requests with no UI changes
- add tests for capturing failed requests and the disabled-captures case
closes#766
Benson Wong
eff9b60434