Import the longest bank-permitted history and surface real provider errors

Manual history imports failed opaquely once a bank capped lookback on an
established consent (N26 rejects date_from beyond ~90 days with
WRONG_TRANSACTIONS_PERIOD). Backfill now requests the documented longest
fetching strategy, reports the coverage the bank actually provided, and
non-2xx responses surface allowlisted documented error codes instead of a
generic fallback. Dead-session codes map to reconnection. Failed syncs
retry hourly so a stale sync banner no longer persists for a day.

internal/app/consent_test.go

@@ -23,7 +23,7 @@ func (b *historyBank) Authorize(_ context.Context, _, _, state string) (string,
 	return "https://bank.example/authorize", nil
 }
 
-func (b *historyBank) Transactions(_ context.Context, account domain.Account, from, to string) ([]domain.Facts, error) {
+func (b *historyBank) Transactions(_ context.Context, account domain.Account, from, to string, _ bool) ([]domain.Facts, error) {
 	b.fromDates = append(b.fromDates, from)
 	var rows []domain.Facts
 	for _, days := range []int{400, 300, 1} {