Add stats block with server-side sharepic image generation

Introduces an `activitypub/stats` block that displays annual Fediverse
statistics as a card or shareable image. The image mode uses a REST
endpoint (`/activitypub/v1/stats/image/{user_id}/{year}`) to generate
a 1200x630 PNG server-side via GD, making it accessible to social
media platforms for OG/link preview cards.

Based on the wrapped block from the fediverse-wrapped-block branch,
renamed from "wrapped" to "stats" for clarity as a standalone feature.

Author: pfefferle

activitypub.php

@@ -55,6 +55,7 @@ function rest_init() {
 	( new Rest\Admin\Actions_Controller() )->register_routes();
 	( new Rest\Admin\Statistics_Controller() )->register_routes();
 	( new Rest\Application_Controller() )->register_routes();
+	( new Rest\Stats_Image_Controller() )->register_routes();
 	( new Rest\Collections_Controller() )->register_routes();
 	( new Rest\Comments_Controller() )->register_routes();
 	( new Rest\Followers_Controller() )->register_routes();

includes/class-blocks.php

@@ -143,6 +143,7 @@ public static function register_blocks() {
 		\register_block_type_from_metadata( ACTIVITYPUB_PLUGIN_DIR . '/build/follow-me' );
 		\register_block_type_from_metadata( ACTIVITYPUB_PLUGIN_DIR . '/build/followers' );
 		\register_block_type_from_metadata( ACTIVITYPUB_PLUGIN_DIR . '/build/posts-and-replies' );
+		\register_block_type_from_metadata( ACTIVITYPUB_PLUGIN_DIR . '/build/stats' );
 
 		// Only register the Following block if the Following feature is enabled.
 		if ( '1' === \get_option( 'activitypub_following_ui', '0' ) ) {