feat: card rail via LNbits fiat providers (Stripe), per operator

A guest may pay a fiat-priced room by card when its owner has opted in and
LNbits core has a fiat provider for that user — resolved through
settings.get_fiat_providers_for_user(owner), the seam lnbits#67's per-user
Stripe Connect credentials will plug into; chatelet stores no credentials.

Both rails now go through create_payment_request: Lightning unchanged
(sats, deposit_sat), card charges the same deposit share of the fiat price
in the room's currency with extra.checkout parameterising the hosted
Stripe page — success/cancel return to {frontend}/chatelet/{room}?checkout=…
&booking=<id>, customer_email, line item, metadata. frontend_url is
allow-listed against the instance's trusted origins (ported from events)
and resolved before the hold so a refused rail never leaves a dead hold.
Core settles the Stripe webhook onto the same invoice queue, so
tasks.on_invoice_paid confirms card bookings unchanged.

BookingRequestData gains payment_method / fiat_provider / frontend_url;
BookingQuote gains fiat_payment_request / fiat_provider / is_fiat and a
nullable payment_request. RPC chatelet_booking_request passes the fields
through. min_lnbits_version → 1.4.1 (events' floor for these APIs).

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>

transport_rpcs.py

@@ -172,7 +172,12 @@ async def handle_booking_request(auth: None, request: NostrRpcRequest) -> dict:
         num_guests=body.get("num_guests", 1),
         guest_contact=body.get("guest_contact"),
         message=body.get("message"),
+        payment_method=body.get("payment_method", "lightning"),
+        fiat_provider=body.get("fiat_provider"),
+        frontend_url=body.get("frontend_url"),
     )
+    # No request host on this door: the checkout returns to the instance root
+    # unless the client names its own (allow-listed) frontend_url.
     quote = await services.request_booking(data)
     return _to_dict(quote)