Fix Salvage Bay drop-off not working by adding config-driven buffer capacity

src/lib/config/BuildingsConfig.h

@@ -1,5 +1,6 @@
 #pragma once
 
+#include <optional>
 #include <string>
 #include <vector>
 
@@ -18,6 +19,10 @@ struct BuildingDef
     // Stored as raw strings here; parsing into per-cell tiles + output ports
     // happens when buildings are placed, not at load time.
     std::vector<std::string> surfaceMask;
+
+    // Output-buffer holding size for buildings without a recipe-driven buffer.
+    // Only the Salvage Bay sets this (REQ-BLD-SALVAGE-BAY).
+    std::optional<int> outputBufferCapacity;
 };
 
 struct BuildingsConfig