feat: per-event payment methods (extra.payment_methods)

Organizers pick which rails an event accepts — Lightning, card (fiat) or
both — instead of a bare "allow fiat" toggle. `extra.payment_methods`
uses the field name upstream v2 (lnbits/events#64) introduces so the
eventual rebase merges cleanly; an empty list keeps the legacy rule
(Lightning always, fiat when allow_fiat), and allow_fiat stays the
fiat-currency carrier, kept in lockstep on save. The effective list is
published as the NIP-52 tag `tickets_payment_methods` so clients render
exactly the buttons the purchase endpoint will accept, and the buyer page
defaults to the first accepted rail (a card-only event never submits
"lightning").

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01EYwoAkZZmXMMmaBp4WGUBo

nostr_publisher.py

@@ -17,7 +17,7 @@ from datetime import datetime, timezone
 from lnbits.core.signers import NostrSigner
 from loguru import logger
 
-from .models import Event
+from .models import Event, effective_payment_methods
 from .nostr.event import NostrEvent
 from .nostr_timestamp import monotonic_created_at
 
@@ -110,6 +110,11 @@ def build_nip52_event(event: Event, pubkey: str) -> NostrEvent:
         tags.append(["tickets_allow_fiat", "true"])
         if event.fiat_currency:
             tags.append(["tickets_fiat_currency", event.fiat_currency])
+    # Rails the organizer accepts, resolved through the same helper the
+    # ticket endpoint enforces with, so a client can render exactly the
+    # buttons that will be accepted (e.g. a card-only event) without a REST
+    # round-trip. Comma-separated, lowercase.
+    tags.append(["tickets_payment_methods", ",".join(effective_payment_methods(event))])
 
     # NIP-52 calendar events are replaceable: this d-tag is republished
     # whenever inventory changes (a ticket sells). Use a strictly-monotonic