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/big_fish.rs

@@ -722,7 +722,7 @@ pub async fn execute_big_fish_action(
         "big_fish_publish_game" => Some("big_fish_publish_game"),
         _ => None,
     };
-    let billing_asset_id = format!("{session_id}:{now}");
+    let billing_asset_id = format!("{}:{}:{}", session_id, action, request_context.request_id());
     let session_operation = async {
         match action.as_str() {
             "big_fish_compile_draft" => {