feat(billing): make metering formula admin-configurable

Allow margin/FX/cost-mode knobs to be overridden via h5_billing_admin_config so memind_adm can adjust DeepSeek billing without editing env.

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

user-auth.mjs

@@ -142,6 +142,7 @@ export function createUserAuth(pool, options = {}) {
     ? options.provisionUserDataSpace
     : null;
   const getMindSearchConfig = typeof options.getMindSearchConfig === 'function' ? options.getMindSearchConfig : null;
+  const billingConfigService = options.billingConfigService ?? null;
   const sessions = new Map();
   const loginFailures = new Map();
 
@@ -1334,7 +1335,9 @@ export function createUserAuth(pool, options = {}) {
       };
     }
     const tokenState = normalizeTokenState(tokenStateRaw);
-    const config = loadBillingConfig();
+    const config = billingConfigService?.getEffectiveBillingConfig
+      ? await billingConfigService.getEffectiveBillingConfig()
+      : loadBillingConfig(env);
     const normalizedRequestId = requestId ? String(requestId).trim() || null : null;
     const now = Date.now();
     const conn = await pool.getConnection();