feat(billing): add metering formula admin tab

Expose margin multiplier, FX rate, and cost-mode settings under 计费中心 so operators can adjust DeepSeek billing without env edits.

Co-authored-by: Cursor <cursoragent@cursor.com>

server/app.mjs

@@ -104,6 +104,7 @@ export function createAdminApp(services) {
     orchestratorObservabilityService,
     personalMemoryCandidateStore,
     skillRuntimeConfigService,
+    billingConfigService,
     wechatScheduleLlmConfigService,
     adminSystemTestService,
     systemTestAccountService,
@@ -628,6 +629,40 @@ export function createAdminApp(services) {
     res.json(await skillRuntimeConfigService.getPublicRuntimeConfig());
   });
 
+  adminApi.get('/billing/config', requireAdmin, async (_req, res) => {
+    if (!billingConfigService?.getAdminConfig) {
+      return res.status(503).json({ message: '计费公式配置服务未启用' });
+    }
+    return res.json(await billingConfigService.getAdminConfig());
+  });
+
+  const updateBillingConfig = async (req, res) => {
+    if (!billingConfigService?.updateAdminConfig) {
+      return res.status(503).json({ message: '计费公式配置服务未启用' });
+    }
+    try {
+      return res.json(await billingConfigService.updateAdminConfig(
+        req.body?.config ?? req.body ?? {},
+        { updatedBy: req.currentUser.id },
+      ));
+    } catch (error) {
+      if (error?.code === 'BILLING_CONFIG_ENV_LOCKED') {
+        return res.status(409).json({ message: error.message, code: error.code });
+      }
+      throw error;
+    }
+  };
+
+  adminApi.put('/billing/config', requireAdmin, updateBillingConfig);
+  adminApi.patch('/billing/config', requireAdmin, updateBillingConfig);
+
+  adminApi.get('/billing/runtime', requireAdmin, async (_req, res) => {
+    if (!billingConfigService?.getRuntimeState) {
+      return res.status(503).json({ message: '计费公式配置服务未启用' });
+    }
+    return res.json(await billingConfigService.getRuntimeState());
+  });
+
   adminApi.get('/system-tests/accounts', requireAdmin, async (_req, res) => {
     if (!systemTestAccountService) {
       return res.status(503).json({ message: '系统测试账号服务未启用' });