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.

tests/npc_schedule_test.gd

@@ -14,6 +14,7 @@ func _run() -> void:
 	_test_sleep_restores_energy()
 	_test_schedule_serialization()
 	_test_sleep_targets_home()
+	_test_household_familiarity()
 
 	if failures.is_empty():
 		print("[TEST] NPC schedule passed")
@@ -181,6 +182,63 @@ func _test_sleep_targets_home() -> void:
 	manager.free()
 
 
+func _test_household_familiarity() -> void:
+	var manager: Node = load("res://simulation/SimulationManager.gd").new()
+	manager.simulation_seed = 700
+	manager.debug_logs = false
+	manager.set_process(false)
+	manager.home_positions = [
+		Vector3(-15.0, 2.0, 7.0),
+		Vector3(-15.0, 2.0, 8.0),
+		Vector3(-8.5, 2.0, 3.0),
+		Vector3(-6.5, 2.0, 1.5),
+		Vector3(20.0, 0.0, 20.0),
+		Vector3(22.0, 0.0, 22.0)
+	]
+	root.add_child(manager)
+
+	var a: SimNPC = manager.npcs[0]
+	var b: SimNPC = manager.npcs[1]
+	var c: SimNPC = manager.npcs[2]
+	var d: SimNPC = manager.npcs[3]
+	var e: SimNPC = manager.npcs[4]
+
+	_check(
+		a.familiarity.has(b.id) and b.familiarity.has(a.id),
+		"NPCs with nearby homes should be mutual household members"
+	)
+	_check(
+		is_equal_approx(float(a.familiarity[b.id]), 0.5),
+		"Household familiarity should start at baseline 0.5"
+	)
+	_check(
+		c.familiarity.has(d.id) and d.familiarity.has(c.id),
+		"Second household pair should also be familiar"
+	)
+	_check(
+		not a.familiarity.has(e.id),
+		"Distant NPCs should not have household familiarity"
+	)
+
+	var saved_json: String = manager.serialize_state()
+	var restored: Node = load("res://simulation/SimulationManager.gd").new()
+	restored.debug_logs = false
+	root.add_child(restored)
+	restored.set_process(false)
+	_check(
+		restored.restore_state_from_json(saved_json),
+		"Familiarity should survive save/load round-trip"
+	)
+	var ra: SimNPC = restored.npcs[0]
+	_check(
+		ra.familiarity.size() > 0,
+		"Restored NPC should retain household familiarity"
+	)
+
+	manager.free()
+	restored.free()
+
+
 func _check(condition: bool, message: String) -> void:
 	if not condition:
 		failures.append(message)