feat: Complete HTML-first architecture implementation with API integration

- Replace value field with html_content for direct HTML storage
- Add original_template field for style detection preservation
- Remove all markdown processing from injector (delete markdown.go)
- Fix critical content extraction/injection bugs in engine
- Add missing UpdateContent PUT handler for content persistence
- Fix API client field names and add updateContent() method
- Resolve content type validation (only allow text/link types)
- Add UUID-based ID generation to prevent collisions
- Complete first-pass processing workflow for unprocessed elements
- Verify end-to-end: Enhancement → Database → API → Editor → Persistence

All 37 files updated for HTML-first content management system.
Phase 3a implementation complete and production ready.

lib/src/core/api-client.js

@@ -33,7 +33,7 @@ export class ApiClient {
         try {
             const payload = {
                 html_markup: htmlMarkup,  // Always send HTML markup - server extracts ID or generates new one
-                value: content,
+                html_content: content,
                 type: type,
                 file_path: this.getCurrentFilePath()  // Always include file path for consistent ID generation
             };
@@ -66,6 +66,40 @@ export class ApiClient {
         }
     }
 
+    async updateContent(contentId, content) {
+        try {
+            const payload = {
+                html_content: content
+            };
+            
+            const response = await fetch(`${this.baseUrl}/${contentId}?site_id=${this.siteId}`, {
+                method: 'PUT',
+                headers: {
+                    'Content-Type': 'application/json',
+                    'Authorization': `Bearer ${this.getAuthToken()}`
+                },
+                body: JSON.stringify(payload)
+            });
+            
+            if (response.ok) {
+                const result = await response.json();
+                console.log(`✅ Content updated: ${contentId}`);
+                return result;
+            } else {
+                console.warn(`⚠️ Update failed (${response.status}): ${contentId}`);
+                return false;
+            }
+        } catch (error) {
+            if (error.name === 'TypeError' && error.message.includes('fetch')) {
+                console.warn(`🔌 API Server not reachable at ${this.baseUrl}`);
+                console.warn('💡 Start full-stack development: just dev');
+            } else {
+                console.error('Failed to update content:', contentId, error);
+            }
+            return false;
+        }
+    }
+
     async getContentVersions(contentId) {
         try {
             const response = await fetch(`${this.baseUrl}/${contentId}/versions?site_id=${this.siteId}`);