feat(skill): 新增多种攻击技能动画与配置

新增冰、火、水等元素的攻击技能动画（.anim）与预制体（.prefab），包括冰球、火球、水球、火墙及不同颜色的箭矢。同时更新技能配置表（SkillSet.ts），将原有技能ID 6002-6004重新命名为更具描述性的名称，并新增技能ID 6005-6008以对应新的技能资源。删除了旧版技能资源文件（b_arrow_* 和 m_water_ball_1）。

assets/resources/game/skill/anm/atk/atk_arrow_green.anim

@@ -1,17 +1,17 @@
 [
   {
     "__type__": "cc.AnimationClip",
-    "_name": "atk_arrow_blue",
+    "_name": "atk_arrow_green",
     "_objFlags": 0,
     "__editorExtras__": {
       "embeddedPlayerGroups": []
     },
     "_native": "",
-    "sample": 24,
+    "sample": 12,
     "speed": 1,
     "wrapMode": 2,
     "enableTrsBlending": false,
-    "_duration": 0.16666666666666666,
+    "_duration": 0.3333333333333333,
     "_hash": 500763545,
     "_tracks": [
       {
@@ -69,25 +69,25 @@
     "__type__": "cc.ObjectCurve",
     "_times": [
       0,
-      0.041666666666666664,
       0.08333333333333333,
-      0.125
+      0.16666666666666666,
+      0.25
     ],
     "_values": [
       {
-        "__uuid__": "3d46f945-3f07-477e-a95a-b49557d552c6@a22e7",
+        "__uuid__": "3d46f945-3f07-477e-a95a-b49557d552c6@1b09a",
         "__expectedType__": "cc.SpriteFrame"
       },
       {
-        "__uuid__": "3d46f945-3f07-477e-a95a-b49557d552c6@20740",
+        "__uuid__": "3d46f945-3f07-477e-a95a-b49557d552c6@341ae",
         "__expectedType__": "cc.SpriteFrame"
       },
       {
-        "__uuid__": "3d46f945-3f07-477e-a95a-b49557d552c6@35944",
+        "__uuid__": "3d46f945-3f07-477e-a95a-b49557d552c6@6459e",
         "__expectedType__": "cc.SpriteFrame"
       },
       {
-        "__uuid__": "3d46f945-3f07-477e-a95a-b49557d552c6@b9343",
+        "__uuid__": "3d46f945-3f07-477e-a95a-b49557d552c6@820a5",
         "__expectedType__": "cc.SpriteFrame"
       }
     ]