fix(grid): persist WHERE filter input across tab switches (closes #210)

whereFilterInput was a component-local ref that got lost when switching
tabs because DataGrid is destroyed and recreated via :key binding.

Store whereInput in the QueryTab state and pass it as initialWhereInput
prop so it survives tab switches.

src/components/grid/DataGrid.vue

@@ -80,6 +80,7 @@ const props = defineProps<{
   connectionId?: string;
   database?: string;
   context?: "results" | "table-data";
+  initialWhereInput?: string;
   tableMeta?: {
     schema?: string;
     tableName: string;
@@ -228,7 +229,7 @@ const orderBySuggestionLeft = ref(0);
 
 const orderByInput = ref("");
 const hasOrderByInput = computed(() => orderByInput.value.trim().length > 0);
-const whereFilterInput = ref("");
+const whereFilterInput = ref(props.initialWhereInput ?? "");
 const hasWhereFilterInput = computed(() => whereFilterInput.value.trim().length > 0);
 
 type LocalColumnFilterDraft = {

src/components/layout/ContentArea.vue

@@ -374,6 +374,7 @@ function onHandleCloseColumnPanel() {
           :loading="activeTab.isExecuting"
           :editable="!!activeTab.tableMeta?.primaryKeys?.length"
           context="table-data"
+          :initial-where-input="activeTab.whereInput"
           :database-type="activeConnection?.db_type"
           :connection-id="activeTab.connectionId"
           :database="activeTab.database"