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/api/handlers.go

@@ -17,6 +17,8 @@ import (
 	"github.com/insertr/insertr/internal/db"
 	"github.com/insertr/insertr/internal/db/postgresql"
 	"github.com/insertr/insertr/internal/db/sqlite"
+	"github.com/insertr/insertr/internal/parser"
+	"golang.org/x/net/html"
 )
 
 // ContentHandler handles all content-related HTTP requests
@@ -232,6 +234,16 @@ func (h *ContentHandler) CreateContent(w http.ResponseWriter, r *http.Request) {
 		siteID = "default" // final fallback
 	}
 
+	// Determine content ID - use provided ID or generate from element context
+	contentID := req.ID
+	if contentID == "" {
+		if req.ElementContext == nil {
+			http.Error(w, "Either ID or element_context required", http.StatusBadRequest)
+			return
+		}
+		contentID = h.generateContentID(req.ElementContext)
+	}
+
 	// Extract user from request using authentication service
 	userInfo, authErr := h.authService.ExtractUserFromRequest(r)
 	if authErr != nil {
@@ -246,7 +258,7 @@ func (h *ContentHandler) CreateContent(w http.ResponseWriter, r *http.Request) {
 	switch h.database.GetDBType() {
 	case "sqlite3":
 		content, err = h.database.GetSQLiteQueries().CreateContent(context.Background(), sqlite.CreateContentParams{
-			ID:           req.ID,
+			ID:           contentID,
 			SiteID:       siteID,
 			Value:        req.Value,
 			Type:         req.Type,
@@ -254,7 +266,7 @@ func (h *ContentHandler) CreateContent(w http.ResponseWriter, r *http.Request) {
 		})
 	case "postgresql":
 		content, err = h.database.GetPostgreSQLQueries().CreateContent(context.Background(), postgresql.CreateContentParams{
-			ID:           req.ID,
+			ID:           contentID,
 			SiteID:       siteID,
 			Value:        req.Value,
 			Type:         req.Type,
@@ -728,3 +740,41 @@ func (h *ContentHandler) versionMatches(version interface{}, contentID, siteID s
 	}
 	return false
 }
+
+// generateContentID creates a content ID from element context using the parser
+func (h *ContentHandler) generateContentID(ctx *ElementContext) string {
+	// Create virtual node for existing parser ID generation
+	virtualNode := &html.Node{
+		Type: html.ElementNode,
+		Data: ctx.Tag,
+		Attr: []html.Attribute{
+			{Key: "class", Val: strings.Join(ctx.Classes, " ")},
+		},
+	}
+
+	// Add parent context as a virtual parent node if provided
+	if ctx.ParentContext != "" && ctx.ParentContext != "content" {
+		parentNode := &html.Node{
+			Type: html.ElementNode,
+			Data: "section",
+			Attr: []html.Attribute{
+				{Key: "class", Val: ctx.ParentContext},
+			},
+		}
+		parentNode.AppendChild(virtualNode)
+		virtualNode.Parent = parentNode
+	}
+
+	// Add text content for hash generation
+	if ctx.OriginalContent != "" {
+		textNode := &html.Node{
+			Type: html.TextNode,
+			Data: ctx.OriginalContent,
+		}
+		virtualNode.AppendChild(textNode)
+	}
+
+	// Use existing parser ID generator
+	idGenerator := parser.NewIDGenerator()
+	return idGenerator.Generate(virtualNode)
+}