feat: add CSV/JSON export buttons to query results and table data view

Export dropdown (CSV/JSON) appears in the WorkspacePanel toolbar when
query results are available, and in the TableDataView toolbar for table
data. Uses the Tauri save dialog for file path selection.

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

src/components/table-viewer/TableDataView.tsx

@@ -9,7 +9,15 @@ import { getTableColumns } from "@/lib/tauri";
 import { useQuery, useQueryClient } from "@tanstack/react-query";
 import { useAppStore } from "@/stores/app-store";
 import { toast } from "sonner";
-import { Save, RotateCcw, Filter, Loader2, Lock } from "lucide-react";
+import { Save, RotateCcw, Filter, Loader2, Lock, Download } from "lucide-react";
+import {
+  DropdownMenu,
+  DropdownMenuContent,
+  DropdownMenuItem,
+  DropdownMenuTrigger,
+} from "@/components/ui/dropdown-menu";
+import { exportCsv, exportJson } from "@/lib/tauri";
+import { save } from "@tauri-apps/plugin-dialog";
 
 interface Props {
   connectionId: string;
@@ -123,6 +131,30 @@ export function TableDataView({ connectionId, schema, table }: Props) {
     setPendingChanges(new Map());
   };
 
+  const handleExport = useCallback(
+    async (format: "csv" | "json") => {
+      if (!data || data.columns.length === 0) return;
+      const ext = format === "csv" ? "csv" : "json";
+      const path = await save({
+        title: `Export as ${ext.toUpperCase()}`,
+        defaultPath: `${table}.${ext}`,
+        filters: [{ name: ext.toUpperCase(), extensions: [ext] }],
+      });
+      if (!path) return;
+      try {
+        if (format === "csv") {
+          await exportCsv(path, data.columns, data.rows as unknown[][]);
+        } else {
+          await exportJson(path, data.columns, data.rows as unknown[][]);
+        }
+        toast.success(`Exported to ${path}`);
+      } catch (err) {
+        toast.error("Export failed", { description: String(err) });
+      }
+    },
+    [data, table]
+  );
+
   const handleApplyFilter = () => {
     setAppliedFilter(filter || undefined);
     setPage(1);
@@ -153,6 +185,28 @@ export function TableDataView({ connectionId, schema, table }: Props) {
         >
           Apply
         </Button>
+        {data && data.columns.length > 0 && (
+          <DropdownMenu>
+            <DropdownMenuTrigger asChild>
+              <Button
+                size="sm"
+                variant="ghost"
+                className="h-6 gap-1 text-xs"
+              >
+                <Download className="h-3 w-3" />
+                Export
+              </Button>
+            </DropdownMenuTrigger>
+            <DropdownMenuContent align="start">
+              <DropdownMenuItem onClick={() => handleExport("csv")}>
+                Export CSV
+              </DropdownMenuItem>
+              <DropdownMenuItem onClick={() => handleExport("json")}>
+                Export JSON
+              </DropdownMenuItem>
+            </DropdownMenuContent>
+          </DropdownMenu>
+        )}
         {pendingChanges.size > 0 && (
           <>
             <Button