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>

ui/frontend/src/lib/active-view/battle.svelte

@@ -20,6 +20,7 @@ viewer keeps its prop-driven contract.
 		fetchBattle,
 		type BattleReport,
 	} from "../../api/battle-fetch";
+	import { isSyntheticGameId } from "../../api/synthetic-report";
 	import { i18n } from "$lib/i18n/index.svelte";
 	import {
 		RENDERED_REPORT_CONTEXT_KEY,
@@ -93,7 +94,14 @@ viewer keeps its prop-driven contract.
 			return;
 		}
 		const client = galaxyClient?.client ?? null;
-		if (!client) {
+		// Synthetic games never publish a GalaxyClient because the
+		// surrounding layout deliberately skips `galaxyClient.set(...)`
+		// on that branch (gateway is not reachable in synthetic mode).
+		// `fetchBattle` short-circuits synthetic ids through the
+		// in-memory fixture map and ignores the client argument, so we
+		// must not wait for the client handle on this path — otherwise
+		// the viewer would sit on `loading` forever.
+		if (!client && !isSyntheticGameId(gameId)) {
 			// Layout populates the client after the boot Promise.all
 			// resolves; stay in `loading` so the effect re-runs once
 			// the handle becomes non-null.