Consolidate spatial docs into universe model

docs/UNIVERSE-MODEL.md

@@ -469,6 +469,13 @@ It also gives a cleaner authority boundary for later scaling:
 - one localspace can become one simulation partition
 - one system can remain a higher-level strategic container
 
+This supports:
+
+- interest management
+- tactical culling
+- isolated combat and logistics spaces
+- future sharding without redefining the gameplay model
+
 ## Non-Goals
 
 This model does not require: