按后台配置扣除创作泥点

前端创作表单泥点预校验改为读取入口契约配置

拼图和抓大鹅初始生成后端扣费改为解析后台配置

汪汪声浪初始三图生成按入口总成本拆分扣费

创作工作台按钮和确认弹窗展示后台配置泥点成本

补充泥点扣费回归测试并同步文档与共享记忆

server-rs/crates/shared-contracts/src/bark_battle.rs

@@ -169,6 +169,8 @@ pub struct BarkBattleImageAssetGenerateRequest {
     pub slot: BarkBattleAssetSlot,
     #[serde(default, skip_serializing_if = "Option::is_none")]
     pub draft_id: Option<String>,
+    #[serde(default, skip_serializing_if = "Option::is_none")]
+    pub billing_purpose: Option<String>,
     pub config: BarkBattleConfigEditorPayload,
 }
 
@@ -823,6 +825,7 @@ mod tests {
         let request = BarkBattleImageAssetGenerateRequest {
             slot: BarkBattleAssetSlot::OpponentCharacter,
             draft_id: Some("bark-battle-draft-1".to_string()),
+            billing_purpose: None,
             config: BarkBattleConfigEditorPayload {
                 title: "汪汪冠军杯".to_string(),
                 description: Some(String::new()),