fix: render empty task list items as checkboxes in note previews

The task-list markdown rule only matched a marker followed by a space
("[ ] text"). markdown-it trims trailing whitespace from inline content,
so an item with no text arrived as exactly "[ ]" and rendered as literal
brackets in the card preview, while the editor showed a checkbox.

Match the marker followed by a space or end-of-content instead, and strip
only what was matched so "[ ]x" glued to text stays literal.

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>

src/lib/utils/markdown.test.ts

@@ -95,6 +95,25 @@ describe('renderMarkdown', () => {
 		expect(html).toContain('disabled');
 		expect(html).toContain('class="task-checkbox"');
 	});
+
+	it('should render an empty task item as a checkbox, not literal brackets', () => {
+		const html = renderMarkdown('- [ ] Train tickets\n- [ ]');
+		expect(html).not.toContain('[ ]');
+		expect(html.match(/type="checkbox"/g)).toHaveLength(2);
+	});
+
+	it('should render an empty checked task item as a checked checkbox', () => {
+		const html = renderMarkdown('- [x]');
+		expect(html).not.toContain('[x]');
+		expect(html).toContain('<input type="checkbox" checked disabled class="task-checkbox">');
+		expect(html).toContain('class="task-list"');
+	});
+
+	it('should not treat brackets glued to text as a task marker', () => {
+		const html = renderMarkdown('- [ ]x');
+		expect(html).not.toContain('type="checkbox"');
+		expect(html).toContain('[ ]x');
+	});
 });
 
 describe('stripMarkdown', () => {

src/lib/utils/markdown.ts

@@ -33,12 +33,16 @@ md.core.ruler.after('inline', 'task-lists', (state) => {
 	for (let i = 0; i < tokens.length; i++) {
 		if (tokens[i].type !== 'inline') continue;
 		const content = tokens[i].content;
-		if (content.startsWith('[ ] ') || content.startsWith('[x] ')) {
+		// markdown-it trims trailing whitespace from inline content, so an item
-			const checked = content.startsWith('[x] ');
+		// with no text after the marker arrives as exactly "[ ]" — match the
+		// marker followed by a space or end-of-content.
+		const marker = /^\[( |x)\](?: |$)/.exec(content);
+		if (marker) {
+			const checked = marker[1] === 'x';
 			const checkbox = checked
 				? '<input type="checkbox" checked disabled class="task-checkbox" /> '
 				: '<input type="checkbox" disabled class="task-checkbox" /> ';
-			tokens[i].content = content.slice(4);
+			tokens[i].content = content.slice(marker[0].length);
 			tokens[i].children = md.parseInline(tokens[i].content, state.env)[0].children;
 			// Prepend checkbox
 			const token = new state.Token('html_inline', '', 0);