feat: add live preview system and enhance dev workflow

- Implement debounced live preview in modal editing (500ms)
- Add LivePreviewManager class with element tracking and restoration
- Enhance modal sizing for comfortable 60-80 character editing
- Add auto-copy plugin to rollup config for seamless development
- Update dev command to automatically sync changes to demo-site

The live preview system provides real-time visual feedback while typing in modals,
showing changes in context without saving. Enhanced dev workflow eliminates manual
build steps, enabling instant iteration during development.

lib/rollup.config.js

@@ -1,5 +1,21 @@
 import { nodeResolve } from '@rollup/plugin-node-resolve';
 import terser from '@rollup/plugin-terser';
+import { execSync } from 'child_process';
+
+// Simple copy plugin to auto-copy to demo-site during development
+function copyToDemo() {
+  return {
+    name: 'copy-to-demo',
+    writeBundle() {
+      try {
+        execSync('cp dist/insertr.js ../demo-site/insertr.js');
+        console.log('📄 Copied to demo-site/insertr.js');
+      } catch (error) {
+        console.warn('⚠️  Failed to copy to demo-site:', error.message);
+      }
+    }
+  };
+}
 
 export default [
   // Development build
@@ -11,7 +27,8 @@ export default [
       name: 'Insertr'
     },
     plugins: [
-      nodeResolve()
+      nodeResolve(),
+      copyToDemo()
     ]
   },
   // Production build (minified)