feat: Add plugin action links and user guide

- Add Settings and Dashboard links to the WordPress Plugins page
- Create comprehensive user guide (USERGUIDE.md) covering:
  - Installation and configuration
  - Managing artists, albums, tracks, and playlists
  - Shortcodes and widgets
  - ActivityPub and WooCommerce integration
  - User library features and troubleshooting

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

includes/Plugin.php

@@ -196,6 +196,34 @@ final class Plugin {
         add_action( 'admin_menu', array( $this, 'add_admin_menu' ) );
         add_action( 'admin_enqueue_scripts', array( $this, 'enqueue_admin_assets' ) );
         add_action( 'wp_enqueue_scripts', array( $this, 'enqueue_frontend_assets' ) );
+
+        // Add settings link to plugins page.
+        add_filter( 'plugin_action_links_' . WP_FEDISTREAM_BASENAME, array( $this, 'add_plugin_action_links' ) );
+    }
+
+    /**
+     * Add action links to the plugins page.
+     *
+     * @param array $links Existing action links.
+     * @return array Modified action links.
+     */
+    public function add_plugin_action_links( array $links ): array {
+        $settings_link = sprintf(
+            '<a href="%s">%s</a>',
+            esc_url( admin_url( 'admin.php?page=fedistream-settings' ) ),
+            esc_html__( 'Settings', 'wp-fedistream' )
+        );
+
+        $dashboard_link = sprintf(
+            '<a href="%s">%s</a>',
+            esc_url( admin_url( 'admin.php?page=fedistream' ) ),
+            esc_html__( 'Dashboard', 'wp-fedistream' )
+        );
+
+        // Add our links at the beginning.
+        array_unshift( $links, $dashboard_link, $settings_link );
+
+        return $links;
     }
 
     /**