chore: rebase onto upstream v1.6.1 + bump to v1.6.1-aio.1

Rebases the aio fork onto upstream v1.6.1 (4bf867e), pulling in:
- fiat checkout + email/Nostr DM ticket notifications (PR #50)
- currency-conversion fix (v1.5.0)
- custom notification subject/body (v1.6.0)
- resend-email button on the ticket list (PR #51)

Notable merges:
- views_api.api_event_update keeps the explicit-field-list gating from
  the aio.4 security fix, with allow_fiat + fiat_currency added so an
  owner editing a fiat-enabled event keeps the fiat config.
- models.PublicEvent now exposes both upstream's fiat fields and our
  location / categories / status fields.
- migrations.py reverts to byte-identical to upstream v1.6.1 (no aio
  entries); fork schema lives in migrations_fork.py (per aiolabs/lnbits#8).
- Lint reformatted with black + ruff to match upstream style.

Contributors entry adds `padreug` (aio fork maintainer).

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

models.py

@@ -140,9 +140,7 @@ class CreateTicket(BaseModel):
         email = values.get("email")
         user_id = values.get("user_id")
         if not user_id and not (name and email):
-            raise ValueError(
-                "Either user_id or both name and email must be provided"
-            )
+            raise ValueError("Either user_id or both name and email must be provided")
         if user_id and (name or email):
             raise ValueError("Cannot provide both user_id and name/email")
         return values