Upgrade PHPStan to 2.x and raise analysis level from 6 to 10

- Bump phpstan/phpstan ^2.0 and szepeviktor/phpstan-wordpress ^2.0
- Move the analysis level into phpstan.neon (single source) and raise it to 10
- Add Val, a runtime coercion helper that narrows untyped WordPress boundary
  values (wpdb rows, REST params, superglobals, options) with explicit checks
  instead of blind casts, plus unit tests
- Type value-object fromRow() params as stdClass (what wpdb returns) and map
  columns through Val so unexpected shapes degrade safely
- Use %i identifier placeholders for table names in all wpdb::prepare() calls
  so every query string is a literal and identifiers are escaped by WordPress;
  raises the minimum WordPress version to 6.2 where %i was introduced
- Guard wpdb::prepare() null result before wpdb::query() in updateTax()
- Fix nullable get_permalink()/strtotime() handling, list types at REST and
  capability call sites, dead null-coalescing on checked superglobals, and
  narrow get_users() results before mapping
- Register Val method names with the ValidatedSanitizedInput sniff so it
  validates the real sanitizer around each superglobal read
- Update repository unit tests for the %i placeholder arguments

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

src/GroupClass/GroupClassPage.php

@@ -10,14 +10,16 @@ class GroupClassPage {
 	/**
 	 * Renders the group-class enrolment shortcode output.
 	 *
-	 * @param array<string, string> $atts Shortcode attributes (unused — reserved for future options).
+	 * @param array<string> $atts Shortcode attributes (unused — reserved for future options).
 	 */
 	public function render( array $atts ): string { // phpcs:ignore Generic.CodeAnalysis.UnusedFunctionParameter.Found
 		if ( ! is_user_logged_in() ) {
+			$permalink = get_permalink();
+
 			return sprintf(
 				'<p>%s <a href="%s">%s</a>.</p>',
 				esc_html__( 'Please', 'unsupervised-schedular' ),
-				esc_url( wp_login_url( get_permalink() ) ),
+				esc_url( wp_login_url( false === $permalink ? '' : $permalink ) ),
 				esc_html__( 'log in to enrol in a class', 'unsupervised-schedular' )
 			);
 		}