Add Gutenberg dynamic-block wrappers for the front-end shortcodes

Wrap the four shortcodes (us_booking, us_student_login,
us_student_register, us_group_classes) in dynamic blocks so pages can be
previewed and styled in the block editor. Front-end rendering delegates
to the same page objects the shortcodes use; in the editor's
block-renderer REST preview a static, script-free BlockPreview is
rendered instead (no live REST calls, redirects, or Stripe.js). The
editor script (vanilla JS, no build step) registers each block with
wp.serverSideRender previews and shortcode transforms; frontend.css is
attached as the block style so previews pick up theme styling.

Resolves #44

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

src/BlockPreview.php

@@ -0,0 +1,114 @@
+<?php
+declare(strict_types=1);
+
+namespace Unsupervised\Schedular;
+
+/**
+ * Static, script-free markup for the editor previews of the front-end blocks.
+ *
+ * The booking and group-class pages are populated by JavaScript on the live
+ * site, and the registration page requires a valid invite token — none of
+ * which exist inside the block editor. These previews reproduce the same
+ * wrapper elements and CSS classes the live pages use, filled with
+ * representative placeholder content, so themes can be styled against
+ * realistic markup without firing REST calls, redirects, or Stripe.js.
+ */
+class BlockPreview {
+
+	public static function booking(): string {
+		$days = [
+			[
+				'label' => __( 'Monday', 'unsupervised-schedular' ),
+				'slots' => [
+					[ '16:00–16:30', 30 ],
+					[ '16:30–17:00', 30 ],
+				],
+			],
+			[
+				'label' => __( 'Wednesday', 'unsupervised-schedular' ),
+				'slots' => [
+					[ '17:00–17:45', 45 ],
+				],
+			],
+		];
+
+		$dayHtml = '';
+		foreach ( $days as $day ) {
+			$slotHtml = '';
+			foreach ( $day['slots'] as $slot ) {
+				$slotHtml .= sprintf(
+					'<div class="us-slot"><span>%s (%d min)</span><button type="button" class="us-book-btn" disabled>%s</button></div>',
+					esc_html( $slot[0] ),
+					(int) $slot[1],
+					esc_html__( 'Book', 'unsupervised-schedular' )
+				);
+			}
+
+			$dayHtml .= sprintf(
+				'<div class="us-day"><h3 class="us-day-heading">%s</h3>%s</div>',
+				esc_html( $day['label'] ),
+				$slotHtml
+			);
+		}
+
+		return sprintf(
+			'<div id="us-booking-app">%s<div id="us-slot-list">%s</div></div>',
+			self::note( __( 'Editor preview — students see live availability on the published page.', 'unsupervised-schedular' ) ),
+			$dayHtml
+		);
+	}
+
+	public static function groupClasses(): string {
+		return sprintf(
+			'<div id="us-group-app">%s<div id="us-group-list"><div class="us-class"><h3>%s</h3><p>%s</p><p>%s</p><p>25.00 CAD</p><button type="button" class="us-enrol-btn" disabled>%s</button></div></div></div>',
+			self::note( __( 'Editor preview — students see live group classes on the published page.', 'unsupervised-schedular' ) ),
+			esc_html__( 'Beginner Group Class', 'unsupervised-schedular' ),
+			esc_html__( 'Saturdays 10:00–11:00', 'unsupervised-schedular' ),
+			esc_html__( 'A sample class shown so the page can be styled.', 'unsupervised-schedular' ),
+			esc_html__( 'Enrol', 'unsupervised-schedular' )
+		);
+	}
+
+	/**
+	 * The live login form renders fine without any request state, so the
+	 * preview includes the real template (the editing user is logged in, which
+	 * would otherwise short-circuit to an "already logged in" message).
+	 */
+	public static function login(): string {
+		$error = '';
+
+		ob_start();
+		include USC_PLUGIN_DIR . 'templates/frontend/login-page.php';
+
+		return self::note( __( 'Editor preview — logged-in visitors are offered a link to the booking page instead.', 'unsupervised-schedular' ) ) . (string) ob_get_clean();
+	}
+
+	public static function registration(): string {
+		$fields  = sprintf(
+			'<p><label for="us-reg-email">%s</label><input type="email" id="us-reg-email" value="student@example.com" readonly></p>',
+			esc_html__( 'Email', 'unsupervised-schedular' )
+		);
+		$fields .= sprintf(
+			'<p><label for="us-reg-name">%s</label><input type="text" id="us-reg-name"></p>',
+			esc_html__( 'Your name', 'unsupervised-schedular' )
+		);
+		$fields .= sprintf(
+			'<p><label for="us-reg-pass">%s</label><input type="password" id="us-reg-pass"></p>',
+			esc_html__( 'Password', 'unsupervised-schedular' )
+		);
+		$fields .= sprintf(
+			'<p><input type="submit" value="%s" disabled></p>',
+			esc_attr__( 'Create Account', 'unsupervised-schedular' )
+		);
+
+		return sprintf(
+			'<div class="us-register-form">%s<form>%s</form></div>',
+			self::note( __( 'Editor preview — the live form requires a valid invite link and lists signup policies.', 'unsupervised-schedular' ) ),
+			$fields
+		);
+	}
+
+	private static function note( string $text ): string {
+		return '<p class="us-editor-note">' . esc_html( $text ) . '</p>';
+	}
+}