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.

admin-spa/src/App.tsx

@@ -261,6 +261,7 @@ import NewsletterSubscribers from '@/routes/Marketing/Newsletter';
 import CampaignsList from '@/routes/Marketing/Campaigns';
 import CampaignEdit from '@/routes/Marketing/Campaigns/Edit';
 import MorePage from '@/routes/More';
+import Help from '@/routes/Help';
 
 // Addon Route Component - Dynamically loads addon components
 function AddonRoute({ config }: { config: any }) {
@@ -583,6 +584,9 @@ function AppRoutes() {
       <Route path="/marketing/campaigns" element={<CampaignsList />} />
       <Route path="/marketing/campaigns/:id" element={<CampaignEdit />} />
 
+      {/* Help - Main menu route with no submenu */}
+      <Route path="/help" element={<Help />} />
+
       {/* Dynamic Addon Routes */}
       {addonRoutes.map((route: any) => (
         <Route