Add per-account-type splitEnabled flag from the catalog

When the master marks an account type splitEnabled=false, big days trade
as one unsplit leg (the legacy one-and-done behavior); min-day bumps are
unaffected. Missing field — older master or pre-toggle cached catalog —
defaults to enabled.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

lib/firm-catalog.ts

@@ -154,7 +154,9 @@ function validatePayload(raw: unknown): FirmCatalogPayload {
                 if (typeof type[key] !== 'number') throw new Error(`account type ${j} is missing ${key}`);
             }
             if (!isStages(type.withdrawalStages)) throw new Error(`account type ${j} has bad withdrawalStages`);
-            return type as unknown as CatalogAccountType;
+            // Lenient like platform: a master from before the split toggle
+            // doesn't send the field, and those account types all split.
+            return { ...type, splitEnabled: type.splitEnabled !== false } as unknown as CatalogAccountType;
         });
 
         return {