feat: seed household familiarity from shared home proximity

NPCs whose home positions are within 4m of each other gain mutual familiarity at baseline 0.5. Stored per NPC as a Dictionary keyed by other npc_id, serialized through NPCStateRecord with backward-compatible fallback for old saves. Household pairs form naturally from the home_positions configuration in main.tscn. Includes save/load round-trip test verifying familiarity persists.

simulation/state/NPCStateRecord.gd

@@ -45,7 +45,8 @@ static func capture(npc: SimNPC) -> NPCStateRecord:
 			"inventory": npc.inventory.duplicate(true),
 			"last_task": String(npc.last_task),
 			"random_seed": str(npc.random_source.seed),
-			"random_state": str(npc.random_source.state)
+			"random_state": str(npc.random_source.state),
+			"familiarity": npc.familiarity.duplicate(true)
 		}
 	)
 
@@ -160,6 +161,9 @@ func restore(debug_logs: bool) -> SimNPC:
 	npc.last_task = StringName(data["last_task"])
 	npc.random_source.state = String(data["random_state"]).to_int()
 	npc.debug_logs = debug_logs
+	var saved_familiarity = data.get("familiarity", {})
+	if saved_familiarity is Dictionary:
+		npc.familiarity = saved_familiarity.duplicate(true)
 	return npc