fix(battle-viewer): unblock synthetic-game battle load

The Phase 28 ConnectRPC migration of the battle viewer added a
guard in `lib/active-view/battle.svelte` that waits for the
surrounding layout to publish a `GalaxyClient` before issuing the
fetch. The in-game shell layout deliberately skips
`galaxyClient.set(...)` on the synthetic branch (gateway is not
reachable in synthetic mode), so for any battle opened from a
synthetic-report game the viewer sat on "loading battle…"
forever — `fetchBattle` was never called, so the synthetic-fixture
short-circuit it carries was unreachable.

Let the guard skip synthetic ids: `fetchBattle` already resolves
those through `lookupSyntheticBattle` and never touches the
client, so its signature widens to `GalaxyClient | null` and the
synthetic path passes `null`. The live path still waits for the
handle as before; a `null` client on the live path now fails
fast with a transport-level `BattleFetchError` instead of silently
sitting on `loading`.

Tests:
- Existing "loading placeholder" smoke now uses a non-synthetic
  game id so it keeps asserting the live-path wait.
- Two new cases pin the synthetic behaviour: missing fixture →
  `battle-not-found`; registered fixture → `BattleViewer` mounts.

Docs:
- `docs/FUNCTIONAL.md` §6.5 still described the pre-Phase-28
  raw REST path. Updated to the signed ConnectRPC command and
  noted the synthetic short-circuit. Russian mirror updated.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

docs/FUNCTIONAL_ru.md

@@ -724,10 +724,13 @@ Battle Viewer — отдельное представление, заменяю
 Сам Viewer — логически изолированный компонент, потребляющий
 `BattleReport` в форме `pkg/model/report/battle.go`. Страница-обёртка
 (`ui/frontend/src/lib/active-view/battle.svelte`) забирает отчёт
-через backend-маршрут
-`GET /api/v1/user/games/{game_id}/battles/{turn}/{battle_id}`,
-который проксирует ответ engine-эндпоинта
-`GET /api/v1/battle/:turn/:uuid`.
+подписанной ConnectRPC-командой `user.games.battle` на
+аутентифицированном edge: gateway переводит верифицированный
+envelope в `GET /api/v1/user/games/{game_id}/battles/{turn}/{battle_id}`
+к backend-у, тот в свою очередь проксирует engine-эндпоинт
+`GET /api/v1/battle/:turn/:uuid`. Для synthetic-игр загрузчик
+короткозамыкает запрос на in-memory карту фикстур, наполненную из
+synthetic-report envelope (см. ниже), и не обращается к gateway.
 
 Визуальная модель — радиальная: планета в центре, расы по внешней
 окружности на равных угловых интервалах, внутри расы — облако