Report Connect Message send failures in messaging reports

[ajeety4]

Product Description

No user facing change.

Bug fixes to the Connect Message path: a send rejected by the Connect API is now recorded as an error on the messaging event instead of being reported as completed, and the Message Event Detail page renders Connect Message rows instead of erroring.

Technical Summary

https://dimagi.atlassian.net/browse/CI-910 - Observed while working on this ticket

Six issues in the Connect Message path:

1. MessageEventDetailReport.rows dereferenced msg after ConnectMessage.DoesNotExist, and never initialised recipient.
   Fix: initialise the placeholders before the lookup, as the CONTENT_EMAIL branch does.
2. ConnectBackend.send returned a bool that send_connect_message discarded, so a rejected send reported success — the subevent stayed IN_PROGRESS and the parent event was marked COMPLETED.
   Fix: the backend raises BackendProcessingException with the status code and body, send_connect_message errors the subevent, and ConnectMessageContent.send completes it.
3. ConnectMessage.messaging_subevent was never set, so the detail report's lookup always missed — why 1 (above point 1) was reachable at all.
   Fix: pass get_sms_message_metadata(logged_subevent), as SMSContent does.
4. log_sms_exception reads msg.couch_id, which ConnectMessage doesn't have, so real exceptions raised AttributeError instead of logging.
   Fix: fall back to message_id.
5. Every send failure was labelled ERROR_CONNECT_GATEWAY, including a missing ConnectIDUserLink or absent couch user.
   Fix: get_connect_error_code maps by exception type; the backend wraps RequestException so network failures still count as gateway errors.
6. ConnectMessageContent hardcoded case_id=None, losing the case association on its subevent.
   Fix: take it from self.case.

ConnectMessageSurveyContent needs no change — it sends via send_first_message, which already passes both metadata and logged_subevent.

Feature Flag

COMMCARE_CONNECT

Safety Assurance

Safety story

Low risk, scoped to the CONTENT_CONNECT path. No migrations.

ConnectBackend.send now raises where it returned False; its only caller already caught Exception, so nothing new escapes. ERROR_CONNECT_GATEWAY is a new value in a CharField with no choices constraint, so existing rows are unaffected.

Verified on a local dev domain against all four row shapes — delivered with and without a linked message, gateway 400 with and without one.

Automated test coverage

• corehq/apps/reports/tests/test_message_event_detail_report.py — detail rows with and without a linked ConnectMessage; the second reproduces the UnboundLocalError.
• corehq/messaging/scheduling/tests/test_content.py::TestConnectMessageContentSend — subevent completed on a 200, errored with the response body on a 400 and propagated to the parent event, message linked to the subevent, case recorded.
• corehq/apps/sms/tests/test_api.py — get_connect_error_code over all three exception classes.

Each test was confirmed to fail on the unfixed code.

QA Plan

None

Rollback instructions

• This PR can be reverted after deploy with no further considerations

Labels & Review

• Risk label is set correctly
• The set of people pinged as reviewers is appropriate for the level of risk of the change