feat: billing system — credits, plans, transactions

DB:
- plans: free/starter/pro/business с ценами и лимитами
- user_subscriptions: подписка пользователя на план
- user_balance: баланс кредитов + monthly reset
- user_transactions: история всех движений кредитов
- credit_costs: image=5, text_post=2, article=5, autopublish=0

Engine:
- services/billing.js: getBalance, check, spend, credit, getTransactions, processMonthlyResets
- routes/billing.js: GET /balance, /transactions, /plans, POST /admin/credit, GET /admin/users
- routes/generate.js: списание кредитов перед генерацией (text_post, article, image)
- index.js: GET /api/billing/plans публично (без auth)

src/routes/billing.js

@@ -0,0 +1,82 @@
+const express = require('express');
+const router  = express.Router();
+const billing = require('../services/billing');
+const { query } = require('../config/db');
+
+function uid(req) { return req.headers['x-user-id'] ? parseInt(req.headers['x-user-id']) : null; }
+
+// GET /api/billing/balance — баланс + план текущего юзера
+router.get('/balance', async (req, res) => {
+  const userId = uid(req);
+  if (!userId) return res.status(401).json({ error: 'x-user-id required' });
+  try {
+    await billing.ensureBalance(userId);
+    const bal = await billing.getBalance(userId);
+    res.json(bal);
+  } catch (err) { res.status(500).json({ error: err.message }); }
+});
+
+// GET /api/billing/transactions — история транзакций
+router.get('/transactions', async (req, res) => {
+  const userId = uid(req);
+  if (!userId) return res.status(401).json({ error: 'x-user-id required' });
+  const limit  = Math.min(parseInt(req.query.limit  || 50), 200);
+  const offset = parseInt(req.query.offset || 0);
+  try {
+    const txs = await billing.getTransactions(userId, { limit, offset });
+    const { rows: [{ total }] } = await query(
+      'SELECT count(*)::int as total FROM user_transactions WHERE user_id=$1', [userId]
+    );
+    res.json({ transactions: txs, total, limit, offset });
+  } catch (err) { res.status(500).json({ error: err.message }); }
+});
+
+// GET /api/billing/plans — все тарифы (публичный)
+router.get('/plans', async (req, res) => {
+  try {
+    const { rows } = await query(
+      'SELECT * FROM plans WHERE is_active=true ORDER BY sort_order'
+    );
+    const { rows: costs } = await query('SELECT * FROM credit_costs ORDER BY operation');
+    res.json({ plans: rows, costs });
+  } catch (err) { res.status(500).json({ error: err.message }); }
+});
+
+// POST /api/billing/admin/credit — начислить кредиты вручную (только admin)
+router.post('/admin/credit', async (req, res) => {
+  const adminId = uid(req);
+  if (!adminId) return res.status(401).json({ error: 'x-user-id required' });
+  const { rows: [admin] } = await query('SELECT is_admin FROM users WHERE id=$1', [adminId]);
+  if (!admin?.is_admin) return res.status(403).json({ error: 'Forbidden' });
+
+  const { user_id, amount, description = 'Ручное начисление от администратора' } = req.body;
+  if (!user_id || !amount) return res.status(400).json({ error: 'user_id и amount обязательны' });
+  try {
+    const result = await billing.credit(user_id, amount, 'bonus', description, { by_admin: adminId });
+    res.json(result);
+  } catch (err) { res.status(500).json({ error: err.message }); }
+});
+
+// GET /api/billing/admin/users — балансы всех пользователей (только admin)
+router.get('/admin/users', async (req, res) => {
+  const adminId = uid(req);
+  if (!adminId) return res.status(401).json({ error: 'x-user-id required' });
+  const { rows: [admin] } = await query('SELECT is_admin FROM users WHERE id=$1', [adminId]);
+  if (!admin?.is_admin) return res.status(403).json({ error: 'Forbidden' });
+  try {
+    const { rows } = await query(`
+      SELECT u.id, u.email, u.name,
+             ub.credits, ub.reset_at,
+             p.name as plan_name, p.code as plan_code, p.price_rub
+      FROM users u
+      LEFT JOIN user_balance ub ON ub.user_id = u.id
+      LEFT JOIN user_subscriptions us ON us.user_id = u.id
+        AND us.status='active' AND (us.expires_at IS NULL OR us.expires_at > NOW())
+      LEFT JOIN plans p ON p.id = us.plan_id
+      ORDER BY u.created_at DESC
+    `);
+    res.json(rows);
+  } catch (err) { res.status(500).json({ error: err.message }); }
+});
+
+module.exports = router;