Initial plugin scaffold: lesson scheduling WordPress plugin

- Custom DB tables for availability slots and lesson bookings
- Instructor (wp-admin) and student (front-end) roles with custom capabilities
- REST API under us-scheduler/v1 for availability CRUD and booking
- [us_booking] and [us_student_login] shortcodes for student front end
- PHPUnit + Brain\Monkey unit test suite (29 tests)
- Gitea Actions CI: lint, PHPStan, tests on PHP 8.1/8.2/8.3, no-debug check
- Feature docs under docs/features/

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

src/Frontend/LoginPage.php

@@ -0,0 +1,44 @@
+<?php
+declare(strict_types=1);
+
+namespace Unsupervised\Schedular\Frontend;
+
+class LoginPage
+{
+    public function render(array $atts): string
+    {
+        if (is_user_logged_in()) {
+            $redirect = esc_url(get_permalink());
+            return sprintf(
+                '<p>%s <a href="%s">%s</a>.</p>',
+                esc_html__('You are already logged in.', 'unsupervised-schedular'),
+                $redirect,
+                esc_html__('View available lessons', 'unsupervised-schedular')
+            );
+        }
+
+        $error    = '';
+        $redirect = sanitize_url(get_permalink() ?? '');
+
+        if (isset($_POST['us_login']) && check_admin_referer('us_student_login')) {
+            $credentials = [
+                'user_login'    => sanitize_user($_POST['log'] ?? ''),
+                'user_password' => $_POST['pwd'] ?? '',
+                'remember'      => isset($_POST['rememberme']),
+            ];
+
+            $user = wp_signon($credentials, false);
+
+            if (is_wp_error($user)) {
+                $error = esc_html__('Invalid username or password.', 'unsupervised-schedular');
+            } else {
+                wp_safe_redirect($redirect);
+                exit;
+            }
+        }
+
+        ob_start();
+        include USC_PLUGIN_DIR . 'templates/frontend/login-page.php';
+        return (string) ob_get_clean();
+    }
+}