Resolves betodealmeida's review comments on PR #41133:
- i18n: wrap all user-facing email strings in gettext with named
placeholders (build_subject / errored section / success + failure bodies).
- Human-readable link expiry via a pluralized, translatable helper, fixing
the sub-hour "0 hours" underreporting.
- Group charts that could not be exported by reason
(no-query-context / timeout / general-exception) instead of a flat
"skipped" list; render one labelled section per reason in the email.
- Replace deprecated datetime.utcnow() with datetime.now(tz=timezone.utc).
- Throttle concurrent exports per user+dashboard via a cache lock: return
202 "already in progress" if one is in flight, clear the lock in the
task's finally block (TTL is the backstop).
- Tests: switch the export API tests to the @with_config decorator; add
unit coverage for grouped errors and the throttle-lock cleanup.
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
cbbf5382e8