Restructure src/ and tests/ from package-by-type to package-by-domain

All classes are now organised by domain (Availability, Booking, Auth).
Each domain package contains its value object, repository, admin controller,
REST endpoint, and any shortcode pages under a matching sub-namespace.
Cross-cutting wiring (Plugin, AdminMenu, RestRegistrar, ShortcodeRegistrar,
Schema) lives at src/ root. Tests mirror the domain structure.

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

src/AdminMenu.php

@@ -0,0 +1,60 @@
+<?php
+declare(strict_types=1);
+
+namespace Unsupervised\Schedular;
+
+use Unsupervised\Schedular\Availability\AvailabilityController;
+use Unsupervised\Schedular\Availability\AvailabilityRepository;
+use Unsupervised\Schedular\Auth\RoleManager;
+use Unsupervised\Schedular\Booking\BookingRepository;
+use Unsupervised\Schedular\Booking\LessonController;
+
+class AdminMenu {
+
+	private AvailabilityController $availabilityController;
+	private LessonController $lessonController;
+
+	public function __construct( AvailabilityRepository $availability, BookingRepository $bookings ) {
+		$this->availabilityController = new AvailabilityController( $availability );
+		$this->lessonController       = new LessonController( $bookings );
+	}
+
+	public function register(): void {
+		add_action( 'admin_menu', [ $this, 'addPages' ] );
+	}
+
+	public function addPages(): void {
+		// Admin-only dashboard: all upcoming lessons.
+		add_menu_page(
+			__( 'Scheduler', 'unsupervised-schedular' ),
+			__( 'Scheduler', 'unsupervised-schedular' ),
+			'manage_options',
+			'us-scheduler',
+			[ $this->lessonController, 'renderAdminDashboard' ],
+			'dashicons-calendar-alt',
+			30
+		);
+
+		// Instructor: manage their own availability.
+		add_menu_page(
+			__( 'My Availability', 'unsupervised-schedular' ),
+			__( 'My Availability', 'unsupervised-schedular' ),
+			RoleManager::CAP_MANAGE_AVAILABILITY,
+			'us-availability',
+			[ $this->availabilityController, 'renderPage' ],
+			'dashicons-clock',
+			31
+		);
+
+		// Instructor: view their upcoming lessons.
+		add_menu_page(
+			__( 'My Lessons', 'unsupervised-schedular' ),
+			__( 'My Lessons', 'unsupervised-schedular' ),
+			RoleManager::CAP_VIEW_LESSONS,
+			'us-my-lessons',
+			[ $this->lessonController, 'renderInstructorLessons' ],
+			'dashicons-welcome-learn-more',
+			32
+		);
+	}
+}