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

frontend/src/lib/api/admin.ts

@@ -244,6 +244,9 @@ export const adminApi = {
     req(`/api/admin/config/${key}`, { method: "DELETE" }),
   testEmail: (): Promise<{ sent: boolean; to: string }> =>
     req("/api/admin/config/test-email", { method: "POST" }),
+  /** The bug-report tracker (E16): answers, takes issues, and is private. */
+  testIssues: (): Promise<{ ok: true; repo: string; url: string | null }> =>
+    req("/api/admin/config/test-issues", { method: "POST" }),
   // --- users & roles ---
   adminAudit: (limit = 500): Promise<AuditListResult> => req(`/api/admin/audit?limit=${limit}`),
   clearAudit: (): Promise<{ cleared: number }> => req("/api/admin/audit", { method: "DELETE" }),