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>

nostr_publisher.py

@@ -78,7 +78,7 @@ def build_nip52_event(event: Event, pubkey: str) -> NostrEvent:
         tags.append(["image", event.banner])
     if event.location:
         tags.append(["location", event.location])
-    for cat in (event.categories or []):
+    for cat in event.categories or []:
         tags.append(["t", cat])
 
     nostr_event = NostrEvent(