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.md

@@ -706,10 +706,14 @@ renders one battle at a time. Entry points:
 The viewer is a logically isolated component that consumes a
 `BattleReport` (shape per `pkg/model/report/battle.go`). The page
 loader (`ui/frontend/src/lib/active-view/battle.svelte`) fetches
-the report through the backend gateway route
-`GET /api/v1/user/games/{game_id}/battles/{turn}/{battle_id}`,
-which forwards verbatim to the engine's
-`GET /api/v1/battle/:turn/:uuid`.
+the report through the signed `user.games.battle` ConnectRPC
+command on the authenticated edge: the gateway translates the
+verified envelope into `GET /api/v1/user/games/{game_id}/battles/{turn}/{battle_id}`
+against the backend, which in turn proxies the engine's
+`GET /api/v1/battle/:turn/:uuid`. For synthetic games the loader
+short-circuits to the in-memory fixture map populated by the
+synthetic-report envelope (see below) and never touches the
+gateway.
 
 Visual model is radial: the planet sits at the centre, races are
 placed at equal angular spacing on an outer ring, and each race is