Keep dunning a bounced debit out of the direct-debit track

Once the direct debit bounced and the board sent the Rücklastschrift reminder,
the claim is expected as a transfer by the deadline that letter states. Three
places still treated it as a claim the mandate covers, and the housekeeper's was
the one the board kept running into: after the reminder's deadline lapsed, the
finding went back to "Lastschrift überfällig -- Einzug prüfen, eine postalische
Mahnung ist hier nicht vorgesehen", for a claim that had just been dunned.

The rule now asks whether the claim was dunned before treating it as one for the
direct debit. If it was, it continues in the ordinary dunning sequence: the
running deadline shows as the usual "Frist läuft noch" note, and once that has
passed the next dunning level comes due. The SEPA-specific pending-reminder
detour that used to cover the deadline window is gone with it -- the ordinary
path reports the same thing.

The SEPA run now skips a dunned claim as well, instead of quietly collecting the
money the letter asked the member to transfer (which can bounce a second time,
with a second fee). The skip is reported like the incomplete mandates are, so
nothing disappears from the run without saying why; the dialog's wording is no
longer specific to mandates.

And a dunning mail asks for a transfer even from a member with an active
mandate. The shipped template spells the bank details out, but the ready-made
{{payment.instructions}} paragraph, offered by the template editor for exactly
this mail, told them "wir ziehen den Betrag ein, du musst nichts weiter tun" --
in the letter demanding payment.

Reverting the sent reminder is what puts the claim back into the direct-debit
run; the read of "dunned" is a sent reminder, not a draft.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

README.md

@@ -291,4 +291,13 @@ only confirming actual dispatch starts the new payment deadline and adds an
 optional fee line item. A claim-level dunning hold suppresses automatic and
 manual reminder preparation until it is removed or expires.
 
+An overdue claim of a member with an active mandate is not dunned but reported as
+a direct debit to look into -- until a reminder for it has actually been sent. A
+sent reminder (typically the "Rücklastschrift" preset for a bounced debit) takes
+that claim off the direct-debit track for good: it is expected as a transfer by
+the stated deadline, so the housekeeper continues it in the ordinary dunning
+sequence, the SEPA run leaves it out and says so, and its dunning mail asks for a
+transfer even though the mandate is still active. Reverting the sent reminder puts
+the claim back into the direct-debit run.
+
 Do not place a real member store inside the source repository.