Clean up legacy code after unified architecture implementation

- Remove obsolete cmd/auto_enhance.go command (replaced by unified enhance)
- Implement EnhanceInPlace method using unified pipeline
- Remove generated demo files from git tracking
- Verify all functionality works after cleanup:
  * go build successful
  * enhance command working correctly
  * unified pipeline (discovery → ID generation → content injection) verified
  * clean command structure (only enhance, serve, restore commands)

The codebase is now clean with no legacy auto-enhance references or stub implementations. All functionality consolidated into the unified Discoverer + Enhancer architecture.

internal/engine/engine.go

@@ -75,6 +75,12 @@ func (e *ContentEngine) ProcessContent(input ContentInput) (*ContentResult, erro
 		}
 	}
 
+	// 5. Inject editor assets for enhancement mode (development)
+	if input.Mode == Enhancement {
+		injector := NewInjector(e.client, input.SiteID)
+		injector.InjectEditorAssets(doc, true, "")
+	}
+
 	return &ContentResult{
 		Document:     doc,
 		Elements:     processedElements,