perf: full-stack performance optimization

Frontend:
- Debounce queryStore tab persistence (remove flush:sync deep watcher)
- Eliminate unnecessary object spreading in connectionStore error handling
- Use in-place delete for completion cache invalidation
- Deduplicate schema cache prefix API calls
- Split echarts, reka-ui, marked, @codemirror/commands into separate chunks
- Lazy-load xlsxExport and markdownTable in DataGrid
- Lazy-load marked parser in UpdateDialog

Backend:
- Replace tokio::sync::Mutex with RwLock for AppState connections/configs
  (60+ concurrent reads no longer block each other)
- Parallelize PostgreSQL DDL metadata queries with tokio::try_join!

src/components/grid/DataGrid.vue

@@ -74,8 +74,6 @@ import {
 } from "@/lib/gridSelection";
 import { buildTableSelectSql, quoteTableIdentifier } from "@/lib/tableSelectSql";
 import { buildDataGridRollbackStatements, buildDataGridSaveStatements, formatGridSqlLiteral } from "@/lib/dataGridSql";
-import { formatMarkdownTable } from "@/lib/markdownTable";
-import { buildXlsxWorkbook } from "@/lib/xlsxExport";
 import {
   matchesRowStatusFilter,
   rowStatusFilterAfterAddingRow,
@@ -2019,6 +2017,7 @@ async function exportMarkdown() {
   try {
     const cols = props.result.columns;
     const visibleRows = displayItems.value.map((item) => item.data);
+    const { formatMarkdownTable } = await import("@/lib/markdownTable");
     const md = formatMarkdownTable({ columns: cols, rows: visibleRows });
     if (await saveFileContent(md, "export.md", "Markdown", "md")) {
       toast(t("grid.exported"));
@@ -2030,6 +2029,7 @@ async function exportMarkdown() {
 
 async function exportXlsx() {
   try {
+    const { buildXlsxWorkbook } = await import("@/lib/xlsxExport");
     const workbook = buildXlsxWorkbook({
       sheetName: props.tableMeta?.tableName || "Export",
       columns: props.result.columns,

src/components/layout/UpdateDialog.vue

@@ -1,7 +1,6 @@
 <script setup lang="ts">
-import { computed } from "vue";
+import { ref, watch } from "vue";
 import { useI18n } from "vue-i18n";
-import { Marked } from "marked";
 import { Loader2 } from "lucide-vue-next";
 import { Button } from "@/components/ui/button";
 import { Dialog, DialogContent, DialogFooter, DialogHeader, DialogTitle } from "@/components/ui/dialog";
@@ -27,12 +26,21 @@ const emit = defineEmits<{
 const { t } = useI18n();
 const isDesktop = isTauriRuntime();
 
-const marked = new Marked({ breaks: true, gfm: true });
+const renderedNotes = ref("");
 
-const renderedNotes = computed(() => {
-  if (!props.updateInfo?.release_notes) return "";
-  return marked.parse(props.updateInfo.release_notes) as string;
-});
+watch(
+  () => props.updateInfo?.release_notes,
+  async (notes) => {
+    if (!notes) {
+      renderedNotes.value = "";
+      return;
+    }
+    const { Marked } = await import("marked");
+    const marked = new Marked({ breaks: true, gfm: true });
+    renderedNotes.value = marked.parse(notes) as string;
+  },
+  { immediate: true },
+);
 </script>
 
 <template>