refactor(engine): 스킬 및 전투 시스템 개선

- SkillData 조정
- CombatCalculator 개선
- ItemService 업데이트
- ProgressService 개선
- SkillService 정리

lib/data/skill_data.dart

@@ -19,7 +19,7 @@ class SkillData {
     mpCost: 10,
     cooldownMs: 3000,
     power: 15,
-    damageMultiplier: 1.5,
+    damageMultiplier: 2.0,
   );
 
   /// Core Dump - 중급 공격
@@ -56,7 +56,7 @@ class SkillData {
     mpCost: 80,
     cooldownMs: 45000,
     power: 60,
-    damageMultiplier: 6.0,
+    damageMultiplier: 4.0,
     selfDamagePercent: 0.1,
   );
 
@@ -68,7 +68,7 @@ class SkillData {
     mpCost: 60,
     cooldownMs: 30000,
     power: 50,
-    damageMultiplier: 5.0,
+    damageMultiplier: 3.5,
   );
 
   /// Inject Code - 방어 무시 공격
@@ -91,7 +91,7 @@ class SkillData {
     mpCost: 30,
     cooldownMs: 10000,
     power: 12,
-    damageMultiplier: 1.2,
+    damageMultiplier: 2.0,
     hitCount: 3,
   );
 
@@ -103,7 +103,7 @@ class SkillData {
     mpCost: 45,
     cooldownMs: 15000,
     power: 10,
-    damageMultiplier: 1.0,
+    damageMultiplier: 2.0,
     hitCount: 5,
   );
 
@@ -139,7 +139,7 @@ class SkillData {
     mpCost: 50,
     cooldownMs: 25000,
     power: 40,
-    damageMultiplier: 3.5,
+    damageMultiplier: 3.2,
     element: SkillElement.chaos,
   );
 
@@ -151,7 +151,7 @@ class SkillData {
     mpCost: 55,
     cooldownMs: 20000,
     power: 18,
-    damageMultiplier: 1.8,
+    damageMultiplier: 2.2,
     hitCount: 3,
   );
 
@@ -212,7 +212,7 @@ class SkillData {
     mpCost: 15,
     cooldownMs: 6000,
     power: 12,
-    damageMultiplier: 1.3,
+    damageMultiplier: 2.0,
   );
 
   /// A/B Test - 이중 공격
@@ -223,7 +223,7 @@ class SkillData {
     mpCost: 35,
     cooldownMs: 12000,
     power: 15,
-    damageMultiplier: 1.5,
+    damageMultiplier: 2.0,
     hitCount: 2,
   );