feat(kanban): tiempo maximo por columna con borde rojo (issue 0089)

Adds column-level max time limit. Cards whose time_in_column_ms exceeds
the limit show a red border + red halo. Columns marked as Done never
trigger the visual regardless of the limit (per spec).

Backend:
- Migration 011_column_max_time.sql adds columns.max_time_minutes
  INTEGER NOT NULL DEFAULT 0 (0 = no limit). Aditiva, idempotente.
- Column struct + ColumnPatch + UpdateColumn handle the new field;
  negatives clamp to 0; listing query includes it.
- handleUpdateColumn (PATCH /api/columns/:id) accepts max_time_minutes
  in the JSON body.

Frontend:
- Column TS interface + UpdateColumnInput updated.
- KanbanColumn context menu: new entry "Tiempo maximo" using
  window.prompt for low-friction config; shows current value when >0.
- KanbanCard receives columnOverdue prop calculated from the column
  state and card.time_in_column_ms; renders red border (var
  --mantine-color-red-6) with 2px width + 2px red halo when overdue.
- data-card-id, data-column-overdue, data-locked attributes on the card
  paper element so e2e tests / scripts can query state.

Tests: TestColumnMaxTimeMinutes_Defaults + _Update verify the schema
default, the clamp on negative input, and that updating max_time leaves
other fields untouched.

Visual regression of the red border kept out of automated e2e because
it requires either clock control or real cards aged > N minutes; will be
verified manually after merge.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

frontend/src/App.tsx

@@ -811,6 +811,19 @@ export function App() {
     }
   }, [reload]);
 
+  const handleSetMaxTimeMinutes = useCallback(async (id: string, max_time_minutes: number) => {
+    setBoard((prev) => {
+      if (!prev) return prev;
+      return { ...prev, columns: prev.columns.map((c) => (c.id === id ? { ...c, max_time_minutes } : c)) };
+    });
+    try {
+      await api.updateColumn(id, { max_time_minutes });
+    } catch (e) {
+      notifications.show({ color: "red", message: (e as Error).message });
+      reload();
+    }
+  }, [reload]);
+
   const handleToggleDone = useCallback(async (id: string, is_done: boolean) => {
     setBoard((prev) => {
       if (!prev) return prev;
@@ -995,6 +1008,7 @@ export function App() {
                       onMoveColumnLocation={handleMoveColumnLocation}
                       onDeleteColumn={handleDeleteColumn}
                       onSetWIPLimit={handleSetWIPLimit}
+                      onSetMaxTimeMinutes={handleSetMaxTimeMinutes}
                       onToggleDone={handleToggleDone}
                       onEditCard={openEditCard}
                       onDeleteCard={handleDeleteCard}
@@ -1263,6 +1277,7 @@ export function App() {
                     onMoveColumnLocation={handleMoveColumnLocation}
                     onDeleteColumn={handleDeleteColumn}
                     onSetWIPLimit={handleSetWIPLimit}
+                      onSetMaxTimeMinutes={handleSetMaxTimeMinutes}
                     onToggleDone={handleToggleDone}
                     onEditCard={openEditCard}
                     onDeleteCard={handleDeleteCard}