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.

.gitignore

@@ -98,11 +98,7 @@ client-dist/
 output/
 
 # Generated demo sites (auto-generated by CLI)
-test-sites/**/*-demo/
-test-sites/**/*-enhanced/
-test-sites/**/*-auto/
-test-sites/**/*-temp/
-test-sites/**/*-full/
+test-sites/**/*_enhanced/
 
 # Air temporary files
 tmp/