feat(diagnostics): send a bug report to a private Gitea issue tracker (E16 S4)

- admin config group "Bug reports": Gitea address, repository, token (secret),
  and "Check the connection" — the repository must answer, take issues and
  be PRIVATE (a report carries its reporter's log); checked on every send too
- POST /api/debug-sessions/{id}/issue sends the SAVED draft: create the issue,
  upload each file on its own request (the measured API), then show the
  screenshots inline; progress is kept in the draft, so a send that stops
  half-way keeps its issue and the retry sends only what is missing; 5 new
  issues an hour per user; audited as issue_create
- the composer: Create issue (only where a tracker is set up, naming the
  repository), a partial-send banner with retry, and a Preview — the tracker's
  own rendering in a sandboxed frame, or the zip's markdown without one
- the recorder's refusals answer in the localized family (debug_session_*,
  screenshot_*, issue(s)_*), not bare codes the UI could only call generic
- a tracker refusal logs the status only: its message can quote the title back

backend/app/audit.py

@@ -58,6 +58,9 @@ class AuditAction:
     DOWNLOAD_CREDENTIAL_DELETE = "download_credential_delete"
     # The log itself was cleared (a single row survives the clear as tamper-evidence)
     AUDIT_CLEAR = "audit_clear"
+    # E16: a user sent a debug session's issue to the tracker — the one act that takes their log
+    # off this instance, so it is recorded (target = the session, summary = the issue's URL).
+    ISSUE_CREATE = "issue_create"
 
 
 def record(