Implement unified Discoverer + Enhancer architecture

- Rename AutoEnhancer to Discoverer with clear element discovery focus
- Implement unified enhancement pipeline in Enhancer:
  * Phase 1: Element Discovery (configurable, respects existing insertr classes)
  * Phase 2: ID Generation via engine
  * Phase 3: Content Injection via engine
- Add EnhancementConfig and DiscoveryConfig for flexible configuration
- Update all method names and references (discoverNode, DiscoveryResult, etc.)
- Support both manual class insertion and automatic discovery
- Maintain single enhance command interface while providing unified internal pipeline
- Update all constructors to use new configuration-based approach

This establishes the clean Discoverer + Enhancer architecture discussed, with discovery as configurable first phase and enhancement as unified pipeline.

cmd/enhance.go

@@ -68,7 +68,7 @@ func runEnhance(cmd *cobra.Command, args []string) {
 	}
 
 	// Create enhancer
-	enhancer := content.NewEnhancer(client, siteID)
+	enhancer := content.NewDefaultEnhancer(client, siteID)
 
 	fmt.Printf("🚀 Starting enhancement process...\n")
 	fmt.Printf("📁 Input: %s\n", inputDir)