enhance: implement dynamic modal repositioning with ResizeObserver

- Add ResizeObserver to automatically detect element height changes during live preview
- Implement repositionModal() to keep modal positioned below expanded content
- Combine modal repositioning with scroll-to-fit for optimal visibility
- Solve UX issue where modal would overlap newly added content

lib/src/ui/form-renderer.js

@@ -7,6 +7,8 @@ class LivePreviewManager {
         this.activeElement = null;
         this.originalContent = null;
         this.originalStyles = null;
+        this.resizeObserver = null;
+        this.onHeightChangeCallback = null;
     }
 
     schedulePreview(element, newValue, elementType) {
@@ -33,6 +35,8 @@ class LivePreviewManager {
 
         // Apply preview styling and content
         this.applyPreviewContent(element, newValue, elementType);
+        
+        // ResizeObserver will automatically detect height changes
     }
 
     extractOriginalContent(element, elementType) {
@@ -101,6 +105,9 @@ class LivePreviewManager {
             this.previewTimeouts.delete(elementId);
         }
 
+        // Stop ResizeObserver
+        this.stopResizeObserver();
+
         // Restore original content
         if (this.originalContent && element === this.activeElement) {
             this.restoreOriginalContent(element);
@@ -138,6 +145,36 @@ class LivePreviewManager {
     setActiveElement(element) {
         this.activeElement = element;
         this.originalContent = null;
+        this.startResizeObserver(element);
+    }
+
+    setHeightChangeCallback(callback) {
+        this.onHeightChangeCallback = callback;
+    }
+
+    startResizeObserver(element) {
+        // Clean up existing observer
+        this.stopResizeObserver();
+
+        // Create new ResizeObserver for this element
+        this.resizeObserver = new ResizeObserver(entries => {
+            // Use requestAnimationFrame to ensure smooth updates
+            requestAnimationFrame(() => {
+                if (this.onHeightChangeCallback && element === this.activeElement) {
+                    this.onHeightChangeCallback(element);
+                }
+            });
+        });
+
+        // Start observing the element
+        this.resizeObserver.observe(element);
+    }
+
+    stopResizeObserver() {
+        if (this.resizeObserver) {
+            this.resizeObserver.disconnect();
+            this.resizeObserver = null;
+        }
     }
 }
 
@@ -169,6 +206,11 @@ export class InsertrFormRenderer {
         // Initialize preview manager for this element
         this.previewManager.setActiveElement(element);
         
+        // Set up height change callback to reposition modal based on new element size
+        this.previewManager.setHeightChangeCallback((changedElement) => {
+            this.repositionModal(changedElement, overlay);
+        });
+
         // Create form
         const form = this.createEditForm(contentId, config, currentContent);
 
@@ -357,7 +399,7 @@ export class InsertrFormRenderer {
     }
 
     /**
-     * Position form relative to element
+     * Position form relative to element and ensure visibility with scroll-to-fit
      */
     positionForm(element, overlay) {
         const rect = element.getBoundingClientRect();
@@ -398,6 +440,55 @@ export class InsertrFormRenderer {
         overlay.style.top = `${top}px`;
         overlay.style.left = `${left}px`;
         overlay.style.zIndex = '10000';
+
+        // Ensure modal is fully visible after positioning
+        this.ensureModalVisible(element, overlay);
+    }
+
+    /**
+     * Reposition modal based on current element size and ensure visibility
+     */
+    repositionModal(element, overlay) {
+        // Wait for next frame to ensure DOM is updated
+        requestAnimationFrame(() => {
+            const rect = element.getBoundingClientRect();
+            const form = overlay.querySelector('.insertr-edit-form');
+            
+            // Calculate new position below the current element boundaries
+            const newTop = rect.bottom + window.scrollY + 10;
+            
+            // Update modal position
+            overlay.style.top = `${newTop}px`;
+            
+            // After repositioning, ensure modal is still visible
+            this.ensureModalVisible(element, overlay);
+        });
+    }
+
+    /**
+     * Ensure modal is fully visible by scrolling viewport if necessary
+     */
+    ensureModalVisible(element, overlay) {
+        // Wait for next frame to ensure DOM is updated
+        requestAnimationFrame(() => {
+            const modal = overlay.querySelector('.insertr-edit-form');
+            const modalRect = modal.getBoundingClientRect();
+            const viewportHeight = window.innerHeight;
+            
+            // Calculate if modal extends below viewport
+            const modalBottom = modalRect.bottom;
+            const viewportBottom = viewportHeight;
+            
+            if (modalBottom > viewportBottom) {
+                // Calculate scroll amount needed with some padding
+                const scrollAmount = modalBottom - viewportBottom + 20;
+                
+                window.scrollBy({
+                    top: scrollAmount,
+                    behavior: 'smooth'
+                });
+            }
+        });
     }
 
     /**