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/architecture.md

@@ -161,8 +161,10 @@ unless noted. The table below is a summary — HTMX fragment endpoints
 | Route | Purpose |
 |---|---|
 | `/healthz` | Liveness (no auth) |
+| `/license` | Embedded `LICENSE` text (no auth) |
 | `/setup/*` | One-time admin bootstrap |
 | `/login`, `/logout` | Session auth |
+| `/account` | 308 redirect to `/settings` (pre-1.2.3 route, kept as a compat shim) |
 | `/status` | Process, cert, socket, PTR checks; machine CPU/memory/network |
 | `/domains`, `/domains/*` | Domain and application CRUD, DKIM, L2 limits |
 | `/domains/import` | Domain import (`POST`; form on the Backup page) |