fix: systematic element matching bug in enhancement pipeline

- Problem: Element ID collisions between similar elements (logo h1 vs hero h1)
  causing content to be injected into wrong elements
- Root cause: Enhancer used naive tag+class matching instead of parser's
  sophisticated semantic analysis for element identification

Systematic solution:
- Enhanced parser architecture with exported utilities (GetClasses, ContainsClass)
- Added FindElementInDocument() with content-based semantic matching
- Replaced naive findAndInjectNodes() with parser-based element matching
- Removed code duplication between parser and enhancer packages

Backend improvements:
- Moved ID generation to backend for single source of truth
- Added ElementContext struct for frontend-backend communication
- Updated API handlers to support context-based content ID generation

Frontend improvements:
- Enhanced getElementMetadata() to extract semantic context
- Updated save flow to handle both enhanced and non-enhanced elements
- Improved API client to use backend-generated content IDs

Result:
- Unique content IDs: navbar-logo-200530 vs hero-title-a1de7b
- Precise element matching using content validation
- Single source of truth for DOM utilities in parser package
- Eliminated 40+ lines of duplicate code while fixing core bug

internal/parser/id_generator.go

@@ -28,7 +28,9 @@ func (g *IDGenerator) Generate(node *html.Node) string {
 	contentHash := g.getContentHash(node)
 
 	baseID := g.createBaseID(context, purpose, contentHash)
-	return g.ensureUnique(baseID)
+	finalID := g.ensureUnique(baseID)
+
+	return finalID
 }
 
 // getSemanticContext determines the semantic context from parent elements
@@ -36,11 +38,11 @@ func (g *IDGenerator) getSemanticContext(node *html.Node) string {
 	// Walk up the tree to find semantic containers
 	parent := node.Parent
 	for parent != nil && parent.Type == html.ElementNode {
-		classes := getClasses(parent)
+		classes := GetClasses(parent)
 
 		// Check for common semantic section classes
 		for _, class := range []string{"hero", "services", "nav", "navbar", "footer", "about", "contact", "testimonial"} {
-			if containsClass(classes, class) {
+			if ContainsClass(classes, class) {
 				return class
 			}
 		}
@@ -68,7 +70,7 @@ func (g *IDGenerator) getSemanticContext(node *html.Node) string {
 // getPurpose determines the purpose/role of the element
 func (g *IDGenerator) getPurpose(node *html.Node) string {
 	tag := strings.ToLower(node.Data)
-	classes := getClasses(node)
+	classes := GetClasses(node)
 
 	// Check for specific CSS classes that indicate purpose
 	for _, class := range classes {