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/utils.go

@@ -6,8 +6,8 @@ import (
 	"golang.org/x/net/html"
 )
 
-// getClasses extracts CSS classes from an HTML node
-func getClasses(node *html.Node) []string {
+// GetClasses extracts CSS classes from an HTML node
+func GetClasses(node *html.Node) []string {
 	classAttr := getAttribute(node, "class")
 	if classAttr == "" {
 		return []string{}
@@ -17,8 +17,8 @@ func getClasses(node *html.Node) []string {
 	return classes
 }
 
-// containsClass checks if a class list contains a specific class
-func containsClass(classes []string, target string) bool {
+// ContainsClass checks if a class list contains a specific class
+func ContainsClass(classes []string, target string) bool {
 	for _, class := range classes {
 		if class == target {
 			return true
@@ -157,3 +157,39 @@ func isSelfClosing(node *html.Node) bool {
 
 	return selfClosingTags[node.Data]
 }
+
+// FindElementInDocument finds a parser element in HTML document tree using semantic matching
+func FindElementInDocument(doc *html.Node, element Element) *html.Node {
+	return findElementWithContext(doc, element)
+}
+
+// findElementWithContext uses the parser's semantic understanding to find the correct element
+func findElementWithContext(node *html.Node, target Element) *html.Node {
+	if node.Type == html.ElementNode && node.Data == target.Tag {
+		classes := GetClasses(node)
+		if ContainsClass(classes, "insertr") {
+			// Content-based validation for precise matching
+			textContent := extractTextContent(node)
+			nodeContent := strings.TrimSpace(textContent)
+			targetContent := strings.TrimSpace(target.Content)
+
+			if nodeContent == targetContent {
+				return node
+			}
+		}
+	}
+
+	// Recursively search children
+	for child := node.FirstChild; child != nil; child = child.NextSibling {
+		if result := findElementWithContext(child, target); result != nil {
+			return result
+		}
+	}
+
+	return nil
+}
+
+// GetAttribute gets an attribute value from an HTML node (exported version)
+func GetAttribute(node *html.Node, key string) string {
+	return getAttribute(node, key)
+}