fix(admin): persist image quota by setting remaining directly

Use PUT setImageQuota so admins can lower remaining below the stored plan
limit; grant-only bonus updates silently no-op when bonus is already zero.

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

server/app.mjs

@@ -1233,6 +1233,25 @@ export function createAdminApp(services) {
     });
   });
 
+  adminApi.put('/users/:userId/image-quota', requireAdmin, async (req, res) => {
+    if (!subscriptionService?.setImageQuota) {
+      return res.status(503).json({ message: '图片额度服务未启用' });
+    }
+    const remaining = req.body?.remaining;
+    const total = req.body?.total;
+    const note = String(req.body?.note ?? '').trim();
+    const result = await subscriptionService.setImageQuota(
+      req.params.userId,
+      {
+        remaining: remaining === undefined || remaining === null ? null : Math.floor(Number(remaining)),
+        total: total === undefined || total === null ? null : Math.floor(Number(total)),
+      },
+      { operatorId: req.currentUser.id, note },
+    );
+    if (!result.ok) return res.status(400).json({ message: result.message });
+    res.json(result);
+  });
+
   adminApi.post('/users/:userId/image-quota/grant', requireAdmin, async (req, res) => {
     if (!subscriptionService?.grantImageQuota) {
       return res.status(503).json({ message: '图片额度服务未启用' });