fix: decode   entities from contenteditable in checklist items

Browsers inject   in contenteditable elements, which was not being
decoded by unlinkifyHtml, causing double-escaped " " to appear in
checklist item text.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

src/lib/utils/checklist.test.ts

@@ -318,4 +318,9 @@ describe('unlinkifyHtml', () => {
 		expect(unlinkifyHtml('&lt;b&gt;bold&lt;/b&gt;')).toBe('<b>bold</b>');
 		expect(unlinkifyHtml('say &quot;hello&quot;')).toBe('say "hello"');
 	});
+
+	it('converts &nbsp; from contenteditable to regular spaces', () => {
+		expect(unlinkifyHtml('hello&nbsp;world')).toBe('hello world');
+		expect(unlinkifyHtml('a&nbsp;&nbsp;b')).toBe('a  b');
+	});
 });

src/lib/utils/checklist.ts

@@ -191,6 +191,7 @@ export function unlinkifyHtml(html: string): string {
 	if (!html) return '';
 	return html
 		.replace(/<[^>]*>/g, '')
+		.replace(/&nbsp;/g, ' ')
 		.replace(/&amp;/g, '&')
 		.replace(/&lt;/g, '<')
 		.replace(/&gt;/g, '>')