修复资产计费边界风险

资产生成预扣费改为 fail-closed，避免钱包异常时继续调用外部生成

新增钱包退款 outbox，退款失败时本地落盘并后台重放

拼图首图后台任务改用 SpacetimeDB claim 表实现跨实例互斥

计费 ledger id 统一绑定 request_id，并让前端重试复用 x-request-id

同步 SpacetimeDB bindings、后端架构文档和 Hermes 决策记录

server-rs/crates/api-server/src/bark_battle.rs

@@ -306,11 +306,12 @@ pub async fn generate_bark_battle_image_asset(
         .filter(|value| !value.is_empty())
         .map(ToString::to_string);
     let points_cost = resolve_bark_battle_image_asset_points_cost(&state, &payload).await;
+    let billing_asset_id = request_context.request_id().to_string();
     let result = execute_billable_asset_operation_with_cost(
         &state,
         &owner_user_id,
         bark_battle_slot_asset_kind(&slot),
-        asset_id.as_str(),
+        billing_asset_id.as_str(),
         points_cost,
         async {
             generate_and_persist_bark_battle_image_asset(