fix: use plain newline for <br> in turndown serialization

Author: Algorithm5838

src/lib/components/common/RichTextInput.svelte

@@ -105,6 +105,12 @@
 		}
 	});
 
+	// Emit a plain newline for <br> instead of the default "  \n" (Markdown hard-break)
+	turndownService.addRule('br', {
+		filter: 'br',
+		replacement: () => '\n'
+	});
+
 	import { onMount, onDestroy, tick, getContext } from 'svelte';
 	import { createEventDispatcher } from 'svelte';