Make WP admins instructors too, and add an Access toggle page

A WordPress administrator previously inherited the studio-admin
capabilities but not `manage_availability`, so the studio owner running
as an admin had no way to reach "My Availability" or act as the
instructor — breaking single-instructor businesses.

Grant the instructor capabilities to administrators as well (via the
existing `user_has_cap` filter), and make both grants — studio-admin and
instructor — independently toggleable from a new Access admin page.

- RoleManager: extract `INSTRUCTOR_CAPS`; apply studio and instructor
  cap sets to administrators, each gated on a stored toggle (default on).
- AccessSettings + templates/admin/access.php: two options
  (`us_admin_grant_studio` / `us_admin_grant_instructor`), gated on the
  core `manage_options` capability so disabling a grant can never lock an
  administrator out of re-enabling it.
- AdminMenu: register the Access page after Studio Settings; keep the
  studio sidebar separator visible for any administrator.
- Tests for the toggles and the new settings reader; docs updated.

Co-Authored-By: Claude Opus 4.8 <[email protected]>

src/Auth/AccessSettings.php

@@ -0,0 +1,67 @@
+<?php
+declare(strict_types=1);
+
+namespace Unsupervised\Schedular\Auth;
+
+/**
+ * Site-owner toggles for whether WordPress administrators automatically receive
+ * the studio-admin and/or instructor capabilities.
+ *
+ * Both default on, preserving the out-of-the-box experience where a single
+ * administrator runs the studio and teaches from one account. The settings page
+ * is gated on `manage_options` (the core WordPress administrator capability,
+ * which the plugin never grants or revokes) so an administrator can always reach
+ * it to re-enable a grant — disabling one can never lock them out.
+ */
+class AccessSettings {
+
+	public const OPT_GRANT_STUDIO     = 'us_admin_grant_studio';
+	public const OPT_GRANT_INSTRUCTOR = 'us_admin_grant_instructor';
+
+	/**
+	 * Whether WordPress administrators implicitly hold the studio-admin
+	 * capabilities (offerings, policies, billing, reports, …).
+	 */
+	public function adminsAreStudioAdmins(): bool {
+		return $this->flag( self::OPT_GRANT_STUDIO );
+	}
+
+	/**
+	 * Whether WordPress administrators implicitly hold the instructor
+	 * capabilities (manage their own availability and lessons).
+	 */
+	public function adminsAreInstructors(): bool {
+		return $this->flag( self::OPT_GRANT_INSTRUCTOR );
+	}
+
+	/**
+	 * Read a stored toggle, defaulting to on so a fresh install keeps the
+	 * single-account behaviour.
+	 */
+	private function flag( string $option ): bool {
+		return '0' !== (string) get_option( $option, '1' );
+	}
+
+	public function renderPage(): void {
+		if ( ! current_user_can( 'manage_options' ) ) {
+			wp_die( esc_html__( 'You do not have permission to manage access settings.', 'unsupervised-schedular' ) );
+		}
+
+		if ( isset( $_POST['usc_action'] ) && check_admin_referer( 'usc_access_action' ) ) {
+			$this->save();
+		}
+
+		$adminsAreStudioAdmins = $this->adminsAreStudioAdmins();
+		$adminsAreInstructors  = $this->adminsAreInstructors();
+
+		include USC_PLUGIN_DIR . 'templates/admin/access.php';
+	}
+
+	private function save(): void {
+		// Nonce is verified by the caller (renderPage) before this method runs.
+		// phpcs:disable WordPress.Security.NonceVerification.Missing
+		update_option( self::OPT_GRANT_STUDIO, isset( $_POST['grant_studio'] ) ? '1' : '0' );
+		update_option( self::OPT_GRANT_INSTRUCTOR, isset( $_POST['grant_instructor'] ) ? '1' : '0' );
+		// phpcs:enable WordPress.Security.NonceVerification.Missing
+	}
+}