feat: implement professional modal editing forms (Phase 1.2)

MAJOR UX IMPROVEMENT: Replace basic prompt() with professional forms

New Features:
- Professional modal overlays with backdrop and ESC/click-outside cancel
- Dynamic form generation based on content type and HTML element
- Smart field detection: H1-H6→text, P→textarea, A→link with URL
- Mobile-responsive form positioning and widths
- Complete CSS styling with focus states and transitions
- Proper save/cancel event handling

Technical Implementation:
- Created lib/src/ui/form-renderer.js with modern ES6+ modules
- Integrated into core editor.js with form renderer instance
- Support for text, textarea, markdown, and link field types
- XSS protection with HTML escaping
- Responsive design: mobile-first form sizing
- Professional styling matching prototype quality

Before: Basic browser prompt() for all editing
After: Content-aware professional modal forms

This brings the library from proof-of-concept to professional-grade
editing experience, closing the major UX gap with the archived prototype.

Phase 1.2 ✅ COMPLETED - Next: Authentication system (Phase 1.1)

lib/src/core/editor.js

@@ -1,3 +1,5 @@
+import { InsertrFormRenderer } from '../ui/form-renderer.js';
+
 /**
  * InsertrEditor - Visual editing functionality
  */
@@ -6,6 +8,7 @@ export class InsertrEditor {
         this.core = core;
         this.options = options;
         this.isActive = false;
+        this.formRenderer = new InsertrFormRenderer();
     }
     
     start() {
@@ -54,29 +57,64 @@ export class InsertrEditor {
     }
     
     openEditor(meta) {
-        const { contentId, contentType, element } = meta;
-        const currentContent = element.textContent.trim();
+        const { element } = meta;
+        const currentContent = this.extractCurrentContent(element);
         
-        // For now, use a simple prompt (will be replaced with proper modal)
-        const newContent = prompt(
-            `Edit ${contentType} content (ID: ${contentId}):`, 
-            currentContent
+        // Show professional form instead of prompt
+        this.formRenderer.showEditForm(
+            meta,
+            currentContent,
+            (formData) => this.handleSave(meta, formData),
+            () => this.handleCancel(meta)
         );
+    }
+    
+    extractCurrentContent(element) {
+        // For links, extract both text and URL
+        if (element.tagName.toLowerCase() === 'a') {
+            return {
+                text: element.textContent.trim(),
+                url: element.getAttribute('href') || ''
+            };
+        }
         
-        if (newContent !== null && newContent !== currentContent) {
-            this.updateContent(meta, newContent);
+        // For other elements, just return text content
+        return element.textContent.trim();
+    }
+    
+    handleSave(meta, formData) {
+        console.log('💾 Saving content:', meta.contentId, formData);
+        
+        // Update element content based on type
+        this.updateElementContent(meta.element, formData);
+        
+        // Close form
+        this.formRenderer.closeForm();
+        
+        // TODO: Save to backend API
+        console.log(`✅ Content saved:`, meta.contentId, formData);
+    }
+    
+    handleCancel(meta) {
+        console.log('❌ Edit cancelled:', meta.contentId);
+    }
+    
+    updateElementContent(element, formData) {
+        if (element.tagName.toLowerCase() === 'a') {
+            // Update link element
+            if (formData.text !== undefined) {
+                element.textContent = formData.text;
+            }
+            if (formData.url !== undefined) {
+                element.setAttribute('href', formData.url);
+            }
+        } else {
+            // Update text content
+            element.textContent = formData.text || '';
         }
     }
     
-    updateContent(meta, newContent) {
-        const { element } = meta;
-        
-        // Update the element content
-        element.textContent = newContent;
-        
-        // TODO: Save to backend API
-        console.log(`💾 Content updated:`, meta.contentId, newContent);
-    }
+    // Legacy method - now handled by handleSave and updateElementContent
     
     addEditorStyles() {
         const styles = `