feat: categories table, API, category field in articles

src/routes/categories.js

@@ -0,0 +1,28 @@
+const express = require('express');
+const router = express.Router();
+const { query } = require('../config/db');
+
+// GET /api/categories
+router.get('/', async (_, res) => {
+  try {
+    const { rows } = await query('SELECT * FROM categories ORDER BY sort_order');
+    res.json(rows);
+  } catch (err) { res.status(500).json({ error: err.message }); }
+});
+
+// GET /api/categories/:slug/articles
+router.get('/:slug/articles', async (req, res) => {
+  try {
+    const limit = Math.min(parseInt(req.query.limit) || 20, 100);
+    const offset = parseInt(req.query.offset) || 0;
+    const { rows } = await query(
+      `SELECT id,slug,title,excerpt,cover_url,tags,category,author,reading_time,published_at
+       FROM articles WHERE status='published' AND category=$1
+       ORDER BY published_at DESC LIMIT $2 OFFSET $3`,
+      [req.params.slug, limit, offset]
+    );
+    res.json(rows);
+  } catch (err) { res.status(500).json({ error: err.message }); }
+});
+
+module.exports = router;