docs: rewrite security/operator docs for the multi-user panel (P2)

The CSRF ADR, guide.md, architecture.md route table, the internal/backup
package comment, roadmap/dmarc-reports admin.dmarc_report_email references,
the e2e coverage summary, and the setupManager/store package comments still
described the pre-1.2.0 single-administrator panel or stale implementation
details. Closes P2 of docs/plans/code-review.md; no behaviour change.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
Co-authored-by: Cursor <cursoragent@cursor.com>

docs/development.md

@@ -265,7 +265,11 @@ operator would actually use.
 **Coverage (summary):** bootstrap → SMTP AUTH → delivery → DKIM verify →
 send-log `queued → sent`; negatives (no AUTH, relay, sender/login mismatch,
 L1/L2 limits, milter fail-open, bad `SELFPOST_HOSTNAME`, session survives
-`docker restart`). Polling with timeouts only — no fixed `sleep`.
+`docker restart`); startup checks that supervisord actually brought up
+OpenDKIM, the panel, and Postfix (`checkSupervisorProcesses`), plus logrotate
+config-mode and forced-rotation checks (`checkLogrotateConfigMode`,
+`checkLogrotateRotation` — [test/e2e/logrotate_check.go](../test/e2e/logrotate_check.go)).
+Polling with timeouts only — no fixed `sleep`.
 
 Requires **Docker + Compose v2** on the machine running the suite.