Premium Analytics: trim dashboard sections API to the server contract

Add a derived section slug to Dashboard_Section and its REST
representation, trim GET /sections to { id, slug, label, order },
retire the per-user section-layout write routes (PUT/DELETE layout,
DELETE sections) and the helpers that served them, and relabel the
woocommerce/store section to Store. Layout persistence stays on core
@wordpress/preferences.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01KKXV17Z2FVzrtTt8zK5RaF

Author: louwie17

projects/packages/premium-analytics/changelog/update-premium-analytics-sections-server-contract

@@ -0,0 +1,4 @@
+Significance: minor
+Type: changed
+
+Dashboard Sections API: expose a derived section slug and trim GET /sections to definitions only ({ id, slug, label, order }), retire the per-user section layout write routes in favor of core preferences persistence, and relabel the WooCommerce section to Store.

projects/packages/premium-analytics/src/class-dashboard-section.php

@@ -30,6 +30,13 @@ final class Dashboard_Section {
 	 */
 	public $id;
 
+	/**
+	 * URL-facing section slug, derived from the identifier.
+	 *
+	 * @var string
+	 */
+	public $slug;
+
 	/**
 	 * Display label.
 	 *
@@ -68,11 +75,24 @@ final class Dashboard_Section {
 	public function __construct( $dashboard_name, $id, $args = array() ) {
 		$this->dashboard_name = $dashboard_name;
 		$this->id             = $id;
+		$this->slug           = self::derive_slug( $id );
 		$this->label          = $id;
 
 		$this->set_props( $args );
 	}
 
+	/**
+	 * Derives the URL-facing slug from a namespaced section identifier.
+	 *
+	 * @param string $id Section identifier, e.g. `analytics/traffic`.
+	 * @return string The segment after the namespace, e.g. `traffic`.
+	 */
+	private static function derive_slug( $id ) {
+		$separator = strpos( (string) $id, '/' );
+
+		return false === $separator ? (string) $id : substr( $id, $separator + 1 );
+	}
+
 	/**
 	 * Returns whether this section should be exposed.
 	 *
@@ -107,6 +127,7 @@ public function get_default_layout() {
 	public function to_array() {
 		return array(
 			'id'    => $this->id,
+			'slug'  => $this->slug,
 			'label' => $this->label,
 			'order' => (int) $this->order,
 		);