fix(sheet): 합계 칸 풍선에 알림 까닭과 식을 함께 (M02 전수 재검증)

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01Tjoit7rxvpLMM7cafeVTo1

ui_template/sheet/ui_template_sheet_render.ts

@@ -240,7 +240,11 @@ export function renderSheet(state: RenderState): HTMLElement {
       cols.forEach((col, j) => {
         const td = bodyCell(`t:${total.id}`, col, j, shown(state.result.합계[total.id]?.[col.id]));
         const formula = totalFormula(total, col);
-        if (formula) td.title = formulaLabel(formula, names);
+        if (formula)
+          td.title = td.classList.contains("is-error")
+            ? `${td.title}
+${formulaLabel(formula, names)}`
+            : formulaLabel(formula, names);
         tr.append(td);
       });
       return tr;