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/components/KanbanCard.tsx

@@ -60,6 +60,7 @@ interface Props {
   users: User[];
   assignee?: User;
   inDoneColumn?: boolean;
+  columnOverdue?: boolean;
   isOverlay?: boolean;
   highlight?: boolean;
 }
@@ -86,6 +87,7 @@ function KanbanCardImpl({
   users,
   assignee,
   inDoneColumn,
+  columnOverdue,
   isOverlay,
   highlight,
 }: Props) {
@@ -162,14 +164,25 @@ function KanbanCardImpl({
     onRemoveSticker?.(card.id, index);
   };
 
+  const borderColorPicked = highlight
+    ? "var(--mantine-color-blue-5)"
+    : columnOverdue
+      ? "var(--mantine-color-red-6)"
+      : card.locked
+        ? "var(--mantine-color-yellow-6)"
+        : colorBorder(card.color);
   const style: React.CSSProperties = {
     transform: CSS.Transform.toString(transform),
     transition,
     opacity: isDragging ? 0.4 : 1,
     background: colorBg(card.color),
-    borderColor: highlight ? "var(--mantine-color-blue-5)" : card.locked ? "var(--mantine-color-yellow-6)" : colorBorder(card.color),
-    borderWidth: highlight || card.locked ? 2 : 1,
-    boxShadow: highlight ? "0 0 0 3px var(--mantine-color-blue-4)" : undefined,
+    borderColor: borderColorPicked,
+    borderWidth: highlight || card.locked || columnOverdue ? 2 : 1,
+    boxShadow: highlight
+      ? "0 0 0 3px var(--mantine-color-blue-4)"
+      : columnOverdue
+        ? "0 0 0 2px var(--mantine-color-red-3)"
+        : undefined,
     filter: isDone ? "brightness(0.55) saturate(0.7)" : undefined,
   };
 
@@ -433,6 +446,9 @@ function KanbanCardImpl({
       p="xs"
       shadow={isOverlay ? "lg" : "xs"}
       radius="md"
+      data-card-id={card.id}
+      data-column-overdue={columnOverdue ? "true" : "false"}
+      data-locked={card.locked ? "true" : "false"}
       onContextMenu={onContextMenu}
       onClick={onCardClickAddSticker}
       onDoubleClick={(e) => {