Export: surface failures to users + log to Azure (sync USFM export)

[henrique221]

Problem

The synchronous USFM export the editor uses (fluent-web useExportUsfm →
POST /project-units/{id}/usfm) has two gaps:

1. fluent-web omits credentials. useExportUsfm.ts is the only API call in
   the app missing credentials: 'include'. It works today only because the
   endpoint is unauthenticated — once fix(auth): require authentication on bibles and USFM routes #189's auth merges, this request 401s and
   the editor export breaks. Must ship with (or before) fix(auth): require authentication on bibles and USFM routes #189's deploy.
2. Failures are invisible. The hook throws a generic
   Error('Failed to export USFM'); the UI surfaces nothing actionable, and the
   API doesn't consistently log the failure to App Insights.

Decision (Kasey, 2026-06-18)

improve the user experience to let them know that an error occurred … it should
log to Azure like other things.

Scope

• fluent-web: add credentials: 'include'; surface a retryable error state in
  ExportProjectDialog.
• fluent-api: log sync-export failures via the standard logger → App Insights
  with project-unit context; stop returning raw error.message/details to the
  client (align with the { message } envelope — breaking change, coordinate
  with fluent-web).

⚠️ Release coupling: the fluent-web credentials fix must land no later than
#189's auth change.

Refs

Follow-up from the security/export audit (#194, PR #189).
Detail: docs/proposals/security-and-export-hardening/02-export-error-ux-and-logging.md.

[henrique221]

Both halves are now up for review:

• fluent-web #312 — send credentials on the export request + surface the server's error message in the dialog: fix(export): send credentials and surface server error on USFM export fluent-web#312
• fluent-api fix(usfm): stop leaking raw error detail in sync export 500s #200 — stop leaking raw error details in the sync export 500s (App Insights logging was already in place): fix(usfm): stop leaking raw error detail in sync export 500s #200

Notes from implementing:

• The dialog already had inline error UI + App Insights logging, so the real user-facing gap was the missing credentials (the fix(auth): require authentication on bibles and USFM routes #189 coupling) + showing the actual message instead of a hardcoded "Export Failed".
• ⚠️ #312 must deploy with or before fix(auth): require authentication on bibles and USFM routes #189's auth, or the editor export 401s.

Keeping this issue open until both PRs merge.

[henrique221]

Done — both halves merged: #200 (API: stop leaking raw error detail in sync export 500s) and eten-tech-foundation/fluent-web#312 (send credentials + surface the server's error message). App Insights logging was already in place. Closing.