feat(skill): add force spawn position setting for skills

add forceStartX and forceStartY properties to control skill spawn position
directly use world coordinates when the values are >=0, otherwise use original offset logic

assets/script/game/skill/Skill.ts

@@ -159,8 +159,17 @@ export class Skill extends ecs.Entity {
             SView.group = caster.box_group
 
             this.add(SView);
-            startPos.x = startPos.x + SView.atk_x * face
-            startPos.y = startPos.y + SView.atk_y
+            // 强制出生点：-1=不强制使用 atk_x/atk_y 偏移，>=0=强制世界坐标
+            if (SView.forceStartX >= 0) {
+                startPos.x = SView.forceStartX;
+            } else {
+                startPos.x = startPos.x + SView.atk_x * face;
+            }
+            if (SView.forceStartY >= 0) {
+                startPos.y = SView.forceStartY;
+            } else {
+                startPos.y = startPos.y + SView.atk_y;
+            }
 
             node.setPosition(startPos);