Add Student Management mini system

Express + MySQL CRUD API for student records, with a plain HTML frontend.

- Single-file backend (server.js) with 5 CRUD routes
- Proper HTTP status codes and a consistent error envelope
- 8-digit ids: 2-digit year + per-year 6-digit counter (e.g. 26000001),
  allocated under a MySQL advisory lock so concurrent inserts cannot collide
- student_db.sql schema and seed data
- .env for credentials; only .env.example is committed

package.json

@@ -0,0 +1,18 @@
+{
+  "name": "api-crud-demo",
+  "version": "1.0.0",
+  "description": "",
+  "main": "server.js",
+  "scripts": {
+    "start": "node server.js",
+    "db:push": "node scripts/init-db.js"
+  },
+  "keywords": [],
+  "author": "",
+  "license": "ISC",
+  "type": "commonjs",
+  "dependencies": {
+    "express": "^5.2.1",
+    "mysql2": "^3.24.4"
+  }
+}