docs: translate the roadmap and frame it for an outside reader

roadmap.md is linked from the README table, so it is a page strangers land on.
Translated in full, with a note up front that none of it is a commitment:
there are no dates, the order is a recommendation, and an item can be dropped
once its plan is written. The note also points at product.md for the opposite
question — what the project deliberately will not do — so absence from the
roadmap is not read as a silent plan.

The model assigned to inbound-relay is dropped from the item; model routing
belongs in development.md, not in a statement of direction.

The README row described the file as internal and Russian. It is now neither.

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

CHANGELOG.md

@@ -21,6 +21,11 @@ Format follows [Keep a Changelog](https://keepachangelog.com/en/1.1.0/); version
   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.
+- [docs/roadmap.md](docs/roadmap.md) is now in English, with a short note on
+  how to read it from outside the project: nothing in it is a commitment, there
+  are no dates, and the stated order is a recommendation. The model assigned to
+  an item is no longer recorded there. The README row no longer calls the file
+  internal and Russian, because it is neither.
 - 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