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>

assets/css/frontend.css

@@ -0,0 +1,35 @@
+.us-login-form label {
+    display: block;
+    margin-bottom: 4px;
+    font-weight: 600;
+}
+
+.us-login-form input[type="text"],
+.us-login-form input[type="password"] {
+    width: 100%;
+    max-width: 340px;
+    padding: 8px;
+    border: 1px solid #ccc;
+    border-radius: 4px;
+}
+
+.us-error {
+    color: #c00;
+    border-left: 4px solid #c00;
+    padding-left: 8px;
+}
+
+#us-booking-app .us-slot {
+    border: 1px solid #ddd;
+    border-radius: 4px;
+    padding: 12px 16px;
+    margin-bottom: 8px;
+    display: flex;
+    justify-content: space-between;
+    align-items: center;
+}
+
+#us-booking-error {
+    color: #c00;
+    margin-top: 8px;
+}