feat(mana): PlayerStats mana_heat/leech+gain_mana/spend_hp_cost+击杀回蓝；SpellContext hp_cost_accum

scripts/autoloads/player_stats.gd

@@ -26,9 +26,15 @@ var resistance:    float = 0.0  # 0.0~1.0
 var mana:       float = 100.0
 var mana_max:   float = 100.0
 var mana_regen: float = 5.0    # 每秒回复
+var mana_heat:  float = 0.0    # 递增蓝耗热值（0=无，1=蓝耗翻倍）
+var mana_leech: float = 0.0    # 击杀回蓝量（换杖/换牌重算）
 
 func _ready() -> void:
 	EventBus.subscribe(EventID.PLAYER_DAMAGED, _on_player_damaged)
+	EventBus.subscribe(EventID.ENEMY_KILLED, _on_enemy_killed)
+
+func _on_enemy_killed(_payload: Dictionary) -> void:
+	gain_mana(mana_leech)
 
 ## 升级曲线：roundf(10 × 1.4^(level-1))，P6-N16
 ## Level 1→2: 10 XP; Level 5→6: ≈ 54 XP
@@ -91,6 +97,22 @@ func regen_mana(delta: float) -> void:
 		return
 	mana = min(mana_max, mana + mana_regen * delta)
 
+## 击杀回蓝（魔力虹吸）
+func gain_mana(n: float) -> void:
+	if n <= 0.0:
+		return
+	mana = min(mana_max, mana + n)
+	stats_changed.emit()
+
+## 主动 HP 代价（infinite_spells / heavy_cost）——直接扣血，不走难度减伤
+func spend_hp_cost(amount: float) -> void:
+	if amount <= 0.0:
+		return
+	hp = max(0.0, hp - amount)
+	stats_changed.emit()
+	if hp <= 0.0:
+		EventBus.emit(EventID.PLAYER_DIED, {})
+
 func _on_player_damaged(payload: Dictionary) -> void:
 	take_damage(float(payload.get("damage", 0.0)))