fix(billing): resolve all audit findings — CSRF, float precision, TOCTOU, error sanitization

- Add CSRF token protection for mock payment (SHA256 + constant-time verify)
- Replace f64 currency conversion with pure integer string parsing (parse_yuan_to_cents)
- Move subscription check inside transaction to prevent TOCTOU race
- Rewrite increment_usage to use atomic SQL (account_id+period_start WHERE)
- Add trade_no format validation in payment callback
- Sanitize error messages to prevent sensitive data leakage
- Use i32::try_from for WeChat amount conversion (prevent truncation)
- Replace window.__ZCLAW_STATS_SYNC_INTERVAL__ with useRef pattern
- Replace eprintln/println with tracing macros in lifecycle
- Remove unused variable in scheduler
- Remove duplicate sha2 and unused hmac from Cargo.toml

desktop/src/App.tsx

@@ -1,4 +1,4 @@
-import { useState, useEffect, useCallback } from 'react';
+import { useState, useEffect, useCallback, useRef } from 'react';
 import { motion, AnimatePresence } from 'framer-motion';
 import './index.css';
 import { Sidebar, MainViewType } from './components/Sidebar';
@@ -54,6 +54,7 @@ function App() {
   const [bootstrapStatus, setBootstrapStatus] = useState('Initializing...');
   const [showOnboarding, setShowOnboarding] = useState(false);
   const [showDetailDrawer, setShowDetailDrawer] = useState(false);
+  const statsSyncRef = useRef<ReturnType<typeof setInterval> | null>(null);
 
   // Hand Approval state
   const [pendingApprovalRun, setPendingApprovalRun] = useState<HandRun | null>(null);
@@ -253,9 +254,8 @@ function App() {
           }
         }, MEMORY_STATS_SYNC_INTERVAL);
 
-        // Store interval for cleanup
-        // @ts-expect-error - Global cleanup reference
-        window.__ZCLAW_STATS_SYNC_INTERVAL__ = statsSyncInterval;
+        // Store interval for cleanup via ref
+        statsSyncRef.current = statsSyncInterval;
       } catch (err) {
         log.warn('Failed to start heartbeat engine:', err);
         // Non-critical, continue without heartbeat
@@ -334,10 +334,8 @@ function App() {
     return () => {
       mounted = false;
       // Clean up periodic stats sync interval
-      // @ts-expect-error - Global cleanup reference
-      if (window.__ZCLAW_STATS_SYNC_INTERVAL__) {
-        // @ts-expect-error - Global cleanup reference
-        clearInterval(window.__ZCLAW_STATS_SYNC_INTERVAL__);
+      if (statsSyncRef.current) {
+        clearInterval(statsSyncRef.current);
       }
     };
   }, [connect, onboardingNeeded, onboardingLoading, isLoggedIn]);