feat: user management — detail view, block/unblock, plan change

routes/admin.js: GET /users/:id (profile+channels+balance+transactions)
  PATCH /users/:id (is_blocked, plan_code, name)
  plan change: cancels active sub → creates new → credits reset
generate.js: check is_blocked before generation → 403 ACCOUNT_BLOCKED
DB: users.is_blocked BOOLEAN DEFAULT false

src/routes/generate.js

@@ -19,6 +19,12 @@ router.post('/', async (req, res) => {
     if (type !== 'topics' && !topic) return res.status(400).json({ error: 'topic is required' });
     if (type === 'post' && !channelId) return res.status(400).json({ error: 'channelId is required for posts' });
 
+    // Проверяем не заблокирован ли пользователь
+    if (userId) {
+      const { rows: [u] } = await require('../config/db').query('SELECT is_blocked FROM users WHERE id=$1', [userId]);
+      if (u?.is_blocked) return res.status(403).json({ error: 'Аккаунт заблокирован', code: 'ACCOUNT_BLOCKED' });
+    }
+
     // Проверка и списание кредитов
     const billingOp = BILLING_OP[type];
     let billingResult = null;