feat: Add in-app documentation system

Phase 1: Core Documentation
- Created docs/ folder with 8 markdown documentation files
- Getting Started, Installation, Troubleshooting, FAQ
- Configuration docs (Appearance, SPA Mode)
- Feature docs (Shop, Checkout)
- PHP registry with filter hook for addon extensibility

Phase 2: Documentation Viewer
- DocsController.php with REST API endpoints
- GET /woonoow/v1/docs - List all docs (with addon hook)
- GET /woonoow/v1/docs/{slug} - Get document content
- Admin SPA /help route with sidebar navigation
- Markdown rendering with react-markdown
- Added Help & Docs to More page for mobile access

Filter Hook: woonoow_docs_registry
Addons can register their own documentation sections.

includes/Api/Routes.php

@@ -24,6 +24,7 @@ use WooNooW\Api\NewsletterController;
 use WooNooW\Api\ModulesController;
 use WooNooW\Api\ModuleSettingsController;
 use WooNooW\Api\CampaignsController;
+use WooNooW\Api\DocsController;
 use WooNooW\Frontend\ShopController;
 use WooNooW\Frontend\CartController as FrontendCartController;
 use WooNooW\Frontend\AccountController;
@@ -165,6 +166,10 @@ class Routes {
             $module_settings_controller = new ModuleSettingsController();
             $module_settings_controller->register_routes();
             
+            // Documentation controller
+            $docs_controller = new DocsController();
+            $docs_controller->register_routes();
+            
             // Frontend controllers (customer-facing)
             ShopController::register_routes();
             FrontendCartController::register_routes();