Fix infinite recursion in markdown parsing

🐛 Critical Fix: Maximum call stack exceeded error
✅ Solution: Properly handle regex match result in parseMarkdownToBlocks()

🔧 Issue:
- line.match(/^#+/)[0].length caused infinite recursion
- Browser crashed when editing rich content with headings

🔧 Fix:
- Store regex match result in variable first
- Add null check before accessing match result
- Prevents stack overflow when parsing markdown headings

⚡ Now safe to edit content with # headings without crashes

demo-site/insertr/insertr.js

@@ -302,7 +302,8 @@ class Insertr {
             // Check for headings
             if (line.match(/^#{1,6}\s/)) {
                 if (currentBlock) blocks.push(currentBlock);
-                const level = line.match(/^#+/)[0].length;
+                const hashMatch = line.match(/^#+/);
+                const level = hashMatch ? hashMatch[0].length : 1;
                 currentBlock = {
                     type: `h${level}`,
                     content: line.replace(/^#+\s*/, '').trim()