feat: load legary reports

ui/frontend/src/routes/lobby/+page.svelte

@@ -194,8 +194,14 @@
 	async function onSyntheticFileChange(
 		event: Event & { currentTarget: HTMLInputElement },
 	): Promise<void> {
+		// Capture the element synchronously: `event.currentTarget`
+		// is nulled by the time any of the awaits below resolve, and
+		// reaching for it from the `finally` block then throws
+		// "null is not an object". The reset still has to happen so
+		// re-selecting the same file fires `change` again.
+		const input = event.currentTarget;
 		syntheticError = null;
-		const file = event.currentTarget.files?.[0];
+		const file = input.files?.[0];
 		if (file === undefined) return;
 		try {
 			const text = await file.text();
@@ -213,7 +219,7 @@
 				syntheticError = "failed to load synthetic report";
 			}
 		} finally {
-			event.currentTarget.value = "";
+			input.value = "";
 		}
 	}