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_luck.gd

@@ -0,0 +1,36 @@
+extends "res://addons/gut/test.gd"
+
+const Luck = preload("res://scripts/state/luck.gd")
+
+
+func _rng(s: int) -> RandomNumberGenerator:
+	var r := RandomNumberGenerator.new()
+	r.seed = s
+	return r
+
+
+func test_roll_base_is_deterministic_for_a_seed():
+	assert_eq(Luck.roll_base(_rng(42), 0), Luck.roll_base(_rng(42), 0))
+
+
+func test_roll_base_stays_in_range():
+	for s in range(1, 30):
+		var v := Luck.roll_base(_rng(s), 0)
+		assert_true(v >= Luck.MIN and v <= Luck.MAX, "luck %d out of range" % v)
+
+
+func test_modifier_shifts_result():
+	# +100 modifier clamps to MAX regardless of rolls.
+	assert_eq(Luck.roll_base(_rng(5), 100), Luck.MAX)
+
+
+func test_drift_stays_within_base_band_and_range():
+	assert_eq(Luck.drift(10, 10, 100), 13)   # capped at base+3
+	assert_eq(Luck.drift(10, 10, -100), 7)    # capped at base-3
+	assert_eq(Luck.drift(20, 19, 100), 20)    # base+3=22 -> clamped to MAX
+
+
+func test_descriptor_bands():
+	assert_eq(Luck.descriptor(4), "Fortune spits on you")
+	assert_eq(Luck.descriptor(5), "The world is not on your side")
+	assert_eq(Luck.descriptor(20), "The dice are kind today")