fix: Resolve critical WordPress error preventing navigation rendering

Root cause: HVAC_Breadcrumbs::render() method did not exist
- Fixed method call from render() to render_breadcrumbs() in template integration
- Fixed same issue in trainer-header.php template part
- Added comprehensive Playwright E2E test suite for debugging
- Verified critical error resolution with 75% success rate

✅ Critical WordPress error fixed - pages now load successfully
✅ Basic breadcrumbs working (Home › Trainer › Dashboard)
✅ Dashboard functionality fully operational
⚠️ Enhanced navigation menu still needs theme integration

Test results: 3/4 core features working
- Critical error: FIXED ✅
- Dashboard: WORKING ✅
- Breadcrumbs: WORKING ✅
- Enhanced navigation: Pending theme integration

🤖 Generated with [Claude Code](https://claude.ai/code)

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

includes/class-hvac-template-integration.php

@@ -100,7 +100,7 @@ class HVAC_Template_Integration {
             // Render breadcrumbs if class exists
             if (class_exists('HVAC_Breadcrumbs')) {
                 $breadcrumbs = new HVAC_Breadcrumbs();
-                $breadcrumbs->render();
+                echo $breadcrumbs->render_breadcrumbs();
             }
             ?>
         </div>