docs(site): edit rules for clarity + cross-links; migrate off rules.txt

Editorial pass over site/ru/rules.md (on top of the verbatim port):
- moved the lore intro to the RU home page, rewritten in a modern voice;
- fixed typos, replaced the TODO/WTF cargo-tech note and the abandoned
  (---ссылка---) marker with the verified mechanic and a real cross-link,
  dropped the report TODO row;
- wove organic intra-page cross-links (#combat, #movement, #victory, ...);
- documented engine nuances verified against the code: ore auto-farming
  and the capital / "запасы промышленности" store (industry capped at
  population); cargo lost with ships destroyed in battle; and that a
  losing race's colonists at a neutral planet are NOT lost — they stay
  aboard (this corrects the audit note, verified in route.go).

Migration: delete game/rules.txt (its content now lives, authoritative,
in site/ru/rules.md) and repoint every reference to it (ui/frontend code
comments + tests, ui/docs, tools, ui/PLAN.md links). Record the
RU-authoritative rule in site/README.md and CLAUDE.md. The English
site/rules.md mirror follows in a separate stage.

CLAUDE.md

@@ -16,6 +16,12 @@ This repository hosts the Galaxy Game project.
   mirrored into `docs/FUNCTIONAL_ru.md` in the same patch (translate
   the changed paragraphs only, do not re-translate the whole file).
   A full re-translation only happens on explicit owner request.
+- `site/ru/rules.md` — the player-facing game rules (ported from the
+  former `game/rules.txt`). **Russian is authoritative here**, inverting
+  the usual English-first rule: the game's rules and lore are
+  Russian-native, so `site/ru/rules.md` leads and the English
+  `site/rules.md` is its mirror. Mirror point edits the same way as
+  `docs/FUNCTIONAL.md`, but RU → EN.
 - `docs/TESTING.md` — testing layers (unit / integration), the
   integration runbook, and the principles every test must follow
   (no-op observability for testcontainers, `t.Fatal` on