feat(grid): show nullable indicator in query result headers

apps/desktop/src/lib/dataGrid/dataGridColumnMetadata.ts

@@ -1,5 +1,12 @@
 import type { ColumnInfo } from "@/types/database";
 
+export type DataGridColumnNullability = "nullable" | "required";
+
+export function resolveDataGridColumnNullability(context: "results" | "table-data" | undefined, column: Pick<ColumnInfo, "is_nullable"> | undefined): DataGridColumnNullability | undefined {
+  if (context !== "results" || !column) return undefined;
+  return column.is_nullable ? "nullable" : "required";
+}
+
 export function resolveDataGridColumnsByResultIndex(options: { resultColumns: readonly string[]; sourceColumns?: readonly (string | undefined)[]; tableColumns: readonly ColumnInfo[] }): Array<ColumnInfo | undefined> {
   const columnsByName = new Map<string, ColumnInfo>();
   for (const column of options.tableColumns) {