feat(client): Luck (deterministic gen/drift/descriptor) + GameState store

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

client/tests/unit/test_game_state.gd

@@ -0,0 +1,30 @@
+extends "res://addons/gut/test.gd"
+
+const GameState = preload("res://scripts/state/game_state.gd")
+
+
+func test_add_item_accumulates():
+	var s = GameState.new()
+	s.add_item("coin", 3)
+	s.add_item("coin", 2)
+	assert_eq(s.inventory["coin"], 5)
+
+
+func test_npc_disposition_clamps():
+	var s = GameState.new()
+	s.set_npc_disposition("oda_fenn", 250)
+	assert_eq(s.npc_dispositions["oda_fenn"], 100)
+
+
+func test_drift_luck_respects_base():
+	var s = GameState.new()
+	s.luck_base = 10
+	s.luck = 10
+	s.drift_luck(100)
+	assert_eq(s.luck, 13)
+
+
+func test_luck_descriptor_delegates():
+	var s = GameState.new()
+	s.luck = 4
+	assert_eq(s.luck_descriptor(), "Fortune spits on you")