feat(iframe): 设计器平衡页增 player_iframe_sec 栏；_save 改合并式修复丢键

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

addons/game_designer/balance_tab.gd

@@ -14,6 +14,7 @@ var _miniboss: SpinBox
 var _boss: SpinBox
 var _aether
 var _status: Label
+var _iframe: SpinBox
 
 func _ready() -> void:
 	add_child(UI.header("⚖ 平衡编辑器 — 难度乘子 & Boss 血量"))
@@ -53,6 +54,11 @@ func _ready() -> void:
 		{"label": "碎片", "min": 0, "max": 9999, "step": 1, "int": true}], "➕ 加行")
 	add_child(_aether)
 	_aether.set_values(_data.get("aether_thresholds", [[1, 0], [5, 3], [10, 8], [15, 14], [20, 20]]))
+	add_child(HSeparator.new())
+	var hf := HBoxContainer.new(); add_child(hf)
+	hf.add_child(UI.cell_label("无敌帧时长(秒) player_iframe_sec"))
+	_iframe = UI.spin(0.0, 2.0, 0.05, float(_data.get("player_iframe_sec", 0.5)))
+	hf.add_child(_iframe)
 	add_child(UI.btn("💾 保存 balance.json", _save))
 	_status = UI.status_label(); add_child(_status)
 
@@ -65,12 +71,11 @@ func _save() -> void:
 	for key in MULT_KEYS:
 		var spins: Array = _mult_spins[key]
 		mults[key] = [spins[0].value, spins[1].value, spins[2].value]
-	var thresholds = _aether.get_values()
-	var out := {
-		"difficulty_mults": mults,
-		"boss_hp": {"4": _miniboss.value, "5": _boss.value},
-		"aether_thresholds": thresholds,
-	}
+	var out: Dictionary = _data.duplicate(true)   # 基底保留未知键（mana_heat/infinite_spells 等）
+	out["difficulty_mults"] = mults
+	out["boss_hp"] = {"4": _miniboss.value, "5": _boss.value}
+	out["aether_thresholds"] = _aether.get_values()
+	out["player_iframe_sec"] = _iframe.value
 	if UI.save_json(PATH, out):
 		UI.set_status(_status, "💾 已保存（重启 F5 生效）")
 	else: