Fix all PHPCS coding standards violations

- Add phpcs.xml.dist: excludes PSR-4 file naming, camelCase naming,
  short array syntax, and redundant per-method/property docblocks
- Fix wp_unslash() on all $_POST reads (LoginPage, AvailabilityController)
- Add phpcs:ignore for password field (must not be sanitized)
- Fix Yoda conditions throughout (AvailabilityRepository, AvailabilityEndpoint,
  BookingEndpoint, AvailabilityController)
- Fix inline comments to end with full stops (AdminMenu)
- Replace short ternary ?: with explicit full ternary (BookingEndpoint)
- Rename $namespace param to $route_namespace (reserved keyword warning)
- Add short descriptions to doc blocks that had tag-only blocks
- Add nonce suppression comment in handleFormAction (nonce verified by caller)
- Update composer.json and CI to use phpcs.xml.dist

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

src/Installer.php

@@ -6,25 +6,23 @@ namespace Unsupervised\Schedular;
 use Unsupervised\Schedular\Data\Schema;
 use Unsupervised\Schedular\Roles\RoleManager;
 
-class Installer
-{
-    public function run(): void
-    {
-        $this->createTables();
-        (new RoleManager())->createRoles();
-        flush_rewrite_rules();
-        update_option('us_schedular_version', USC_VERSION);
-    }
+class Installer {
 
-    private function createTables(): void
-    {
-        global $wpdb;
-        $charset = $wpdb->get_charset_collate();
+	public function run(): void {
+		$this->createTables();
+		( new RoleManager() )->createRoles();
+		flush_rewrite_rules();
+		update_option( 'us_schedular_version', USC_VERSION );
+	}
 
-        require_once ABSPATH . 'wp-admin/includes/upgrade.php';
+	private function createTables(): void {
+		global $wpdb;
+		$charset = $wpdb->get_charset_collate();
 
-        foreach (Schema::tables($wpdb->prefix, $charset) as $sql) {
-            dbDelta($sql);
-        }
-    }
+		require_once ABSPATH . 'wp-admin/includes/upgrade.php';
+
+		foreach ( Schema::tables( $wpdb->prefix, $charset ) as $sql ) {
+			dbDelta( $sql );
+		}
+	}
 }