Introduces `PendingStore.nowRfc3339()` to consistently generate RFC3339
timestamps with second granularity. This avoids potential issues with
sub-second precision in filenames and aligns with common timestamp
formatting practices. The helper function is used in `CaseDetailScreen`
and `RecordingViewModel` to replace direct calls to
`Instant.now().toString()`. A new unit test verifies the expected
behavior of the helper function.
Brummel
9cc0946f90