feat(kanban): archive automatico para cards Done +30 dias (issue 0092)

Adds an archive layer separate from the trash. Cards in is_done columns
that have been there for more than 30 days are auto-archived on the next
board load (throttled to once every 30 minutes). Archived cards leave
the board but stay in the DB and are listed in a new sidebar drawer
"Hecho (archivo)" below the existing Papelera, with a one-click restore.

Schema (migration 012_card_archived.sql):
- ALTER TABLE cards ADD COLUMN archived_at TEXT;
- NULL = active, ISO timestamp = archived. Independent from deleted_at.

Backend:
- Card.ArchivedAt + JSON; ListCardsWithTime filters archived_at IS NULL.
- New methods: ArchiveCard, UnarchiveCard, ListArchivedCards,
  AutoArchiveDoneOlderThan.
- New endpoints: GET /api/archive, POST /api/cards/:id/archive,
  POST /api/cards/:id/unarchive.
- handleGetBoard invokes maybeAutoArchive (atomic throttle, 30 min sweep,
  30 day cutoff). Errors logged but never block the board response.

Frontend:
- Card type + api.ts add the new field and helpers.
- App.tsx state for archive list, reload, archive/unarchive handlers.
- New sidebar drawer with toggle, count badge, restore button.
- KanbanCard gains an "Archivar" menu item (gated on isDone +
  onArchive prop) for manual archiving of any done card.

Tests:
- Playwright e2e/archive.spec.ts: manual archive via menu, drawer
  toggle, unarchive. Picks a done card via /api/board introspection so
  it stays stable regardless of board state.
- Auto-archive of >30d cards: not under e2e (real time travel needed);
  covered by code review of the SQL query and the throttle.

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

frontend/src/api.ts

@@ -107,6 +107,18 @@ export function purgeCard(id: string): Promise<void> {
   return fetchJSON(`/cards/${id}/purge`, { method: "DELETE" });
 }
 
+export function listArchive(): Promise<Card[]> {
+  return fetchJSON("/archive");
+}
+
+export function archiveCard(id: string): Promise<void> {
+  return fetchJSON(`/cards/${id}/archive`, { method: "POST" });
+}
+
+export function unarchiveCard(id: string): Promise<void> {
+  return fetchJSON(`/cards/${id}/unarchive`, { method: "POST" });
+}
+
 export function moveCard(id: string, column_id: string, ordered_ids: string[]): Promise<void> {
   return fetchJSON(`/cards/${id}/move`, {
     method: "POST",