refactor: 调整 Markdown 编辑器高度为自适应填充

src/lib/components/admin/MarkdownEditor.svelte

@@ -91,15 +91,16 @@
 			boxShadow: '0 0 0 3px rgba(65, 155, 56, 0.08)'
 		},
 		'.cm-content': {
-			minHeight: '400px',
+			minHeight: '100%',
 			padding: '12px 14px',
 			lineHeight: '1.8'
 		},
 		'.cm-scroller': {
 			overflow: 'auto',
-			minHeight: '400px'
+			minHeight: '100%'
 		},
 		'.cm-gutters': {
+			minHeight: '100%',
 			backgroundColor: 'rgba(0, 0, 0, 0.03)',
 			color: 'rgba(0, 0, 0, 0.4)',
 			borderRight: '1px solid rgba(0, 0, 0, 0.12)',