feat: Implement OAuth license activation flow

- Add LicenseConnect.tsx focused OAuth confirmation page in customer SPA
- Add /licenses/oauth/validate and /licenses/oauth/confirm API endpoints
- Update App.tsx to render license-connect outside BaseLayout (no header/footer)
- Add license_activation_method field to product settings in Admin SPA
- Create LICENSING_MODULE.md with comprehensive OAuth flow documentation
- Update API_ROUTES.md with license module endpoints

admin-spa/src/routes/Appearance/Pages/store/usePageEditorStore.ts

@@ -60,6 +60,7 @@ export interface PageItem {
     slug?: string;
     title: string;
     url?: string;
+    isFrontPage?: boolean;
     isSpaLanding?: boolean;
 }