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

src/services/apiClient.test.ts

@@ -66,6 +66,9 @@ describe('apiClient', () => {
       dispatchEvent: dispatchEventMock,
       localStorage: createLocalStorageMock(),
     });
+    vi.stubGlobal('crypto', {
+      randomUUID: () => '11111111-2222-3333-4444-555555555555',
+    });
     fetchMock.mockReset();
     dispatchEventMock.mockReset();
     clearStoredAccessToken({ emit: false });
@@ -121,6 +124,7 @@ describe('apiClient', () => {
         credentials: 'same-origin',
         headers: expect.objectContaining({
           Authorization: 'Bearer expired-token',
+          'x-request-id': 'web-11111111-2222-3333-4444-555555555555',
           'x-genarrative-response-envelope': 'v1',
         }),
       }),
@@ -140,6 +144,7 @@ describe('apiClient', () => {
         credentials: 'same-origin',
         headers: expect.objectContaining({
           Authorization: 'Bearer fresh-token',
+          'x-request-id': 'web-11111111-2222-3333-4444-555555555555',
         }),
       }),
     );