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/api.ts

@@ -38,6 +38,7 @@ export interface UpdateColumnInput {
   width?: number;
   wip_limit?: number;
   is_done?: boolean;
+  max_time_minutes?: number;
 }
 
 export function updateColumn(id: string, patch: UpdateColumnInput): Promise<void> {