Fix/disable table comment for unsupported db (#518)

* fix(structure-editor): disable table comment input for databases that don't support comments (e.g. SQLite)

## 背景说明
SQLite 不支持表注释（COMMENT），但表注释输入框始终可编辑。用户修改注释后，SQL 预览显示暂无变更且应用变更按钮不可用，造成困惑的 UX。

## 修改内容
- 新增 isTableCommentDisabled 计算属性，基于 structureCapabilities.comment 控制禁用状态
- 表注释 Input 添加 :disabled 绑定，禁用时输入框变灰不可编辑
- 禁用时在输入框右侧显示 Info 图标，hover 显示 Tooltip 说明
- 三语言（zh-CN / en / es）新增 tableCommentUnsupported 翻译

## 影响范围
- SQLite、DuckDB 及未知数据库类型：输入框被禁用 + Tooltip 提示
- MySQL、PostgreSQL、ClickHouse 等支持注释的数据库：完全不受影响
- 后端 generate_comment_ddl 已有对等过滤（仅 Postgres/Oracle/ClickHouse 生成 COMMENT SQL）

## 测试
- 建议补充：dbType 为 sqlite 时 isTableCommentDisabled 为 true 的单元测试

* test(structure-editor): add tests for table comment disabled state and unsupported DB capabilities

apps/desktop/src/components/structure/TableStructureEditor.vue

@@ -12,6 +12,7 @@ import {
   ChevronDown,
   ChevronUp,
   Database,
+  Info,
   KeyRound,
   Loader2,
   Maximize2,
@@ -28,6 +29,7 @@ import {
   DropdownMenuTrigger,
 } from "@/components/ui/dropdown-menu";
 import { Popover, PopoverContent, PopoverTrigger } from "@/components/ui/popover";
+import { Tooltip, TooltipContent, TooltipTrigger } from "@/components/ui/tooltip";
 import { SearchableSelect } from "@/components/ui/searchable-select";
 import { Select, SelectContent, SelectItem, SelectTrigger, SelectValue } from "@/components/ui/select";
 import { useConnectionStore } from "@/stores/connectionStore";
@@ -134,6 +136,7 @@ function onIndexColResize(e: MouseEvent, col: number) {
 const connection = computed(() => (props.connectionId ? store.getConfig(props.connectionId) : undefined));
 const databaseType = computed(() => connection.value?.db_type);
 const structureCapabilities = computed(() => getTableStructureCapabilities(databaseType.value));
+const isTableCommentDisabled = computed(() => !structureCapabilities.value.comment);
 const dataTypeOptions = computed(() => DATA_TYPE_OPTIONS[databaseType.value ?? ""] ?? []);
 
 const indexTypesByDb: Record<string, string[]> = {
@@ -509,7 +512,14 @@ watch(
         v-model="tableComment"
         :placeholder="t('structureEditor.tableCommentPlaceholder')"
         class="h-6 max-w-[320px] text-[11px]"
+        :disabled="isTableCommentDisabled"
       />
+      <Tooltip v-if="isTableCommentDisabled">
+        <TooltipTrigger as-child>
+          <Info class="h-4 w-4 shrink-0 text-muted-foreground" />
+        </TooltipTrigger>
+        <TooltipContent>{{ t("structureEditor.tableCommentUnsupported") }}</TooltipContent>
+      </Tooltip>
     </div>
 
     <div v-if="loading" class="flex min-h-0 flex-1 items-center justify-center gap-2 text-sm text-muted-foreground">