feat: PHP API foundation - router, config, helpers, SM-2 algorithm

edu/api/helpers.php

@@ -0,0 +1,41 @@
+<?php
+header('Content-Type: application/json; charset=utf-8');
+
+function json_ok($data) {
+    echo json_encode($data, JSON_UNESCAPED_UNICODE);
+    exit;
+}
+
+function json_error($message, $code = 400) {
+    http_response_code($code);
+    echo json_encode(['error' => $message], JSON_UNESCAPED_UNICODE);
+    exit;
+}
+
+function require_auth() {
+    if (empty($_SESSION['user_id'])) {
+        json_error('Nicht angemeldet', 401);
+    }
+    return $_SESSION['user_id'];
+}
+
+function require_admin() {
+    require_auth();
+    if (empty($_SESSION['is_admin'])) {
+        json_error('Keine Admin-Berechtigung', 403);
+    }
+    return $_SESSION['user_id'];
+}
+
+function get_method() {
+    return $_SERVER['REQUEST_METHOD'];
+}
+
+function get_json_body() {
+    $body = file_get_contents('php://input');
+    return json_decode($body, true) ?: [];
+}
+
+function get_param($name, $default = null) {
+    return $_GET[$name] ?? $default;
+}