Complete Age lifecycle management (#8)

docs/PORTING.md

@@ -46,6 +46,8 @@ acceptance issue and all required implementation issues are complete.
 Age references use UUIDs rather than dimension keys. The server-owned Age
 registry maps each stable identity to its immutable definition and runtime
 dimension, keeping saved books valid if an Age is migrated or regenerated.
+Operational lifecycle and unload behavior are documented in
+[AGES.md](AGES.md).
 
 The core mod must remain usable without Create, Ponder, or Immersive Portals.
 The built-in legacy animation is the dependency-free destination preview.