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

lib/src/core/api-client.js

@@ -58,27 +58,39 @@ export class ApiClient {
         }
     }
     
-    async createContent(contentId, content, type) {
+    async createContent(contentId, content, type, elementContext = null) {
         try {
+            const payload = {
+                value: content,
+                type: type
+            };
+            
+            if (contentId) {
+                // Enhanced site - provide existing ID
+                payload.id = contentId;
+            } else if (elementContext) {
+                // Non-enhanced site - provide context for backend ID generation
+                payload.element_context = elementContext;
+            } else {
+                throw new Error('Either contentId or elementContext must be provided');
+            }
+            
             const response = await fetch(`${this.baseUrl}?site_id=${this.siteId}`, {
                 method: 'POST',
                 headers: {
                     'Content-Type': 'application/json',
                     'Authorization': `Bearer ${this.getAuthToken()}`
                 },
-                body: JSON.stringify({ 
-                    id: contentId, 
-                    value: content,
-                    type: type 
-                })
+                body: JSON.stringify(payload)
             });
             
             if (response.ok) {
-                console.log(`✅ Content created: ${contentId} (${type})`);
-                return true;
+                const result = await response.json();
+                console.log(`✅ Content created: ${result.id} (${result.type})`);
+                return result;
             } else {
-                console.warn(`⚠️ Create failed (${response.status}): ${contentId}`);
-                return false;
+                console.warn(`⚠️ Create failed (${response.status}): ${contentId || 'backend-generated'}`);
+                return null;
             }
         } catch (error) {
             if (error.name === 'TypeError' && error.message.includes('fetch')) {