fix: 修复 generateGitignore 函数中的换行符语法错误

使用 \n 转义字符替代实际的换行符，避免 JavaScript 语法错误。

🤖 Generated with [Claude Code](https://claude.com/claude-code)

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

Author: chao5go

tools/gitignore-generator/app.html

@@ -185,9 +185,7 @@ <h1>Gitignore 生成器</h1>
             function generateGitignore() {
                 const selected = Array.from(document.querySelectorAll('.checkbox-group input:checked'))
                     .map(input => input.value);
-                const output = selected.map(key => `# ${key}
-` + GITIGNORE_TEMPLATES[key]).join('
-');
+                const output = selected.map(key => `# ${key}\n` + GITIGNORE_TEMPLATES[key]).join('\n\n');
                 document.getElementById('gitignore-output').value = output.trim();
             }