fix: 修复空状态显示问题，添加DDL编辑功能

- 修复无数据时重复显示空状态的问题
- 将DDL展示改为可编辑的textarea
- 优化空状态UI样式和提示文案

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

web/src/views/database/database.css

@@ -30,13 +30,69 @@
   @apply border-b border-dark-600 hover:bg-dark-600/50 transition-colors;
 }
 
-/* 空状态 */
+/* 空状态（已不使用） */
 .empty-state {
-  @apply py-16 text-center text-gray-500;
+  @apply py-16 text-center;
+  display: flex;
+  flex-direction: column;
+  align-items: center;
+  justify-content: center;
+}
+
+/* 自定义空状态盒子 */
+.empty-box {
+  min-height: 340px;
+  display: flex;
+  flex-direction: column;
+  align-items: center;
+  justify-content: center;
+}
+
+.empty-icon {
+  width: 100px;
+  height: 100px;
+  display: flex;
+  align-items: center;
+  justify-content: center;
+  background: linear-gradient(135deg, #1f2937, #111827);
+  border-radius: 24px;
+  margin-bottom: 20px;
+}
+
+.empty-icon i {
+  font-size: 40px;
+  color: #6b7280;
+}
+
+.empty-text {
+  color: #d1d5db;
+  font-size: 1.25rem;
+  font-weight: 500;
+  margin-bottom: 8px;
+}
+
+.empty-tip {
+  color: #6b7280;
+  font-size: 0.875rem;
 }
 
 .empty-state-icon {
-  @apply text-4xl mb-4 block;
+  font-size: 3rem;
+  margin-bottom: 1rem;
+  display: block;
+  color: #4b5563;
+}
+
+.empty-state-title {
+  color: #d1d5db;
+  font-size: 1.25rem;
+  font-weight: 500;
+}
+
+.empty-state-hint {
+  color: #6b7280;
+  font-size: 0.875rem;
+  margin-top: 0.5rem;
 }
 
 /* 表格复选框 */