docs: translate security.md and the last Russian source comments

security.md is linked from the README documentation table and now from
SECURITY.md, so a reader following either link landed in a Russian document
while everything around it was English. Translated in full; the requirements,
the accepted risks, and the CSRF ADR are unchanged in substance.

The reviewing model is no longer named in the text — that the pre-release
review ran, and when, is what a reader needs; who ran it is process detail
kept in development.md.

extract-cert.sh keeps its spec 10.3 quotation, translated. In sasl.go the
quotation from the closed plan is dropped rather than translated: rendered in
English it restated the sentence it hung off.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

CHANGELOG.md

@@ -15,6 +15,17 @@ Format follows [Keep a Changelog](https://keepachangelog.com/en/1.1.0/); version
 
 ### Changed
 
+- [docs/security.md](docs/security.md) is now in English, matching the rest of
+  the published docs — it is linked from the README table and from
+  `SECURITY.md`, so a reader following either landed in Russian. Content is
+  unchanged: same requirements, same accepted risks, same ADR. The reviewing
+  model is no longer named in the text; the fact that a pre-release review ran,
+  and its date, stay.
+- The two remaining Russian source comments are in English:
+  `deploy/traefik/extract-cert.sh` (quote from spec 10.3) and
+  `internal/app/sasl.go`, where the quotation from the closed plan is dropped
+  rather than translated — rendered in English it restated the sentence it was
+  attached to.
 - The panel's **Account** entry is now called **Settings** — nav link, page
   heading, and browser title. The route stays `/account`, so existing links
   and bookmarks are unaffected.