ui/synthetic-report: dev-only legacy report loader on lobby

Adds api/synthetic-report.ts, an in-memory registry + JSON->GameReport
decoder for synthetic-mode game sessions. The lobby grows a
import.meta.env.DEV-gated "Synthetic test reports" section with a
JSON file picker; loading a file registers the decoded report under
a synthetic-<uuid> id and navigates to /games/<id>/map.

The in-game shell layout detects the synthetic id range, takes the
report straight from the registry via gameState.initSynthetic, and
deliberately skips both galaxyClient.set and orderDraft.bindClient.
Order auto-sync stays silent: scheduleSync already short-circuits on
non-UUID game ids, and without a bound client the network path is
unreachable. applyOrderOverlay continues to project locally-valid
draft commands onto the rendered report so renames / production
choices / route edits are visible immediately.

A page reload loses the in-memory entry and redirects to /lobby —
synthetic mode is a debug affordance, not a session.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

ui/frontend/src/routes/games/[id]/+layout.svelte

@@ -44,6 +44,7 @@ fresh.
 -->
 <script lang="ts">
 	import { onDestroy, onMount, setContext } from "svelte";
+	import { goto } from "$app/navigation";
 	import { page } from "$app/state";
 	import Header from "$lib/header/header.svelte";
 	import Sidebar from "$lib/sidebar/sidebar.svelte";
@@ -83,6 +84,10 @@ fresh.
 	import { createEdgeGatewayClient } from "../../../api/connect";
 	import { GalaxyClient } from "../../../api/galaxy-client";
 	import { GATEWAY_BASE_URL, GATEWAY_RESPONSE_PUBLIC_KEY } from "$lib/env";
+	import {
+		getSyntheticReport,
+		isSyntheticGameId,
+	} from "../../../api/synthetic-report";
 
 	let { children } = $props();
 
@@ -167,6 +172,36 @@ fresh.
 
 	onMount(() => {
 		(async (): Promise<void> => {
+			// DEV-only synthetic-report path. The lobby's "Load
+			// synthetic report" affordance navigates here with a
+			// `synthetic-<uuid>` id and the matching report
+			// pre-registered in an in-memory map. A page reload
+			// loses the map entry; that case redirects to /lobby
+			// so the user reloads the JSON.
+			if (isSyntheticGameId(gameId)) {
+				const report = getSyntheticReport(gameId);
+				if (report === undefined) {
+					await goto("/lobby");
+					return;
+				}
+				try {
+					const { cache } = await loadStore();
+					await Promise.all([
+						gameState.initSynthetic({ cache, gameId, report }),
+						orderDraft.init({ cache, gameId }),
+					]);
+					// Deliberately no `galaxyClient.set` and no
+					// `orderDraft.bindClient`: synthetic mode never
+					// sends to the gateway. The auto-sync pipeline
+					// already short-circuits via the UUID guard in
+					// `scheduleSync`, but skipping the bind keeps
+					// the path simple to reason about.
+				} catch (err) {
+					gameState.failBootstrap(describeBootstrapError(err));
+				}
+				return;
+			}
+
 			if (
 				session.keypair === null ||
 				session.deviceSessionId === null ||