refactor: remove legacy parser system and migrate to unified engine

- Remove internal/parser package and all legacy ID generation logic
- Update enhancer and auto_enhancer to use unified engine functions
- Migrate utility functions (FindViableChildren, HasEditableContent) to engine
- Create stub enhancer implementation that uses unified engine architecture
- Ensure all enhancement workflows now go through single unified system
- Remove parser dependencies and consolidate content processing logic

This completes the cleanup phase - all components now use unified engine
instead of fragmented ID generation systems.

internal/content/auto_enhancer.go

@@ -7,20 +7,18 @@ import (
 	"path/filepath"
 	"strings"
 
-	"github.com/insertr/insertr/internal/parser"
+	"github.com/insertr/insertr/internal/engine"
 	"golang.org/x/net/html"
 )
 
 // AutoEnhancer handles automatic enhancement of HTML files
 type AutoEnhancer struct {
-	parser *parser.Parser
+	// Remove parser dependency - auto enhancement is now self-contained
 }
 
 // NewAutoEnhancer creates a new AutoEnhancer instance
 func NewAutoEnhancer() *AutoEnhancer {
-	return &AutoEnhancer{
-		parser: parser.New(),
-	}
+	return &AutoEnhancer{}
 }
 
 // AutoEnhanceResult contains statistics about auto-enhancement
@@ -133,7 +131,7 @@ func (ae *AutoEnhancer) enhanceNode(node *html.Node, result *EnhancementResult,
 
 	// Check if this is a container that should use expansion
 	if ae.isGoodContainer(node) {
-		viableChildren := parser.FindViableChildren(node)
+		viableChildren := engine.FindViableChildren(node)
 		if len(viableChildren) >= 2 || (aggressive && len(viableChildren) >= 1) {
 			// Add insertr class to container for expansion
 			ae.addInsertrClass(node)
@@ -232,9 +230,9 @@ func (ae *AutoEnhancer) isGoodIndividualElement(node *html.Node) bool {
 	return ae.hasEditableContent(node)
 }
 
-// hasEditableContent uses the parser's enhanced detection logic
+// hasEditableContent uses the engine's enhanced detection logic
 func (ae *AutoEnhancer) hasEditableContent(node *html.Node) bool {
-	return parser.HasEditableContent(node)
+	return engine.HasEditableContent(node)
 }
 
 // hasInsertrClass checks if a node already has the insertr class