Initial commit: 金牛集团贷款档案管理系统

导入现有代码与文档，排除 data/uploads 运行时数据。

app/auth.php

@@ -0,0 +1,43 @@
+<?php
+declare(strict_types=1);
+
+require_once __DIR__ . '/db.php';
+
+if (session_status() === PHP_SESSION_NONE) {
+    session_start();
+}
+
+function currentUser(): ?array
+{
+    if (empty($_SESSION['uid'])) {
+        return null;
+    }
+    $stmt = db()->prepare('SELECT id, username, role, created_at FROM users WHERE id = :id');
+    $stmt->execute([':id' => (int)$_SESSION['uid']]);
+    $u = $stmt->fetch();
+    return $u ?: null;
+}
+
+function isAdmin(): bool
+{
+    $u = currentUser();
+    return $u && $u['role'] === 'admin';
+}
+
+function requireLogin(): void
+{
+    if (!currentUser()) {
+        header('Location: index.php?action=login');
+        exit;
+    }
+}
+
+function requireAdmin(): void
+{
+    requireLogin();
+    if (!isAdmin()) {
+        http_response_code(403);
+        echo 'Forbidden';
+        exit;
+    }
+}