feat: multi-ticket purchases as N rows sharing one payment_hash

Replaces the previous "one row, N seats via extra.quantity" model
with proper one-row-per-attendee semantics. Each attendee gets a
unique scannable id; the door PUT /register/{ticket_id} marks
them registered independently — so a buyer can purchase 3 tickets,
hand 2 QRs to friends arriving separately, and each attendee can
enter on their own schedule.

Schema (migrations_fork.py m002):
- ticket.payment_hash: new TEXT column shared across all rows of
  a multi-ticket purchase. Backfilled `payment_hash = id` for
  pre-migration rows (id WAS the payment_hash by invariant).

Wire:
- TicketPaymentRequest grows `ticket_ids: list[str]` so the
  webapp gets every scannable id back in the create response.
- POST /tickets/{event_id}/{payment_hash} polling endpoint now
  reports `ticket_ids` (every row) + keeps `ticket_id` for
  back-compat.
- api_ticket_create loops quantity times; the first row reuses
  payment_hash as id (preserves legacy `id == payment_hash`
  invariant for single-ticket purchases), the rest get
  urlsafe_short_hash() uuids.

Payment flow:
- on_invoice_paid fetches all rows by payment_hash and marks each
  paid via set_ticket_paid, which now increments event.sold by 1
  per row (was N per row via extra.quantity — simpler now). The
  per-event asyncio lock still serializes counter + republish so
  concurrent multi-ticket purchases for the same event don't
  reorder the published Nostr state.
- Each paid row triggers its own send_ticket_notification_in_
  background call — no-op for buyers without nostr_identifier /
  email, useful when the buyer set those on the row.

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

crud.py

@@ -41,8 +41,19 @@ async def create_ticket(
     email: str | None = None,
     user_id: str | None = None,
     extra: dict | None = None,
+    ticket_id: str | None = None,
 ) -> Ticket:
+    """Persist one ticket row.
+
+    `payment_hash` is the LNbits invoice hash shared across all rows
+    of a multi-ticket purchase. `ticket_id` is the row primary key /
+    scannable id; defaults to `payment_hash` for single-ticket
+    purchases so the legacy id == payment_hash invariant holds.
+    Multi-ticket callers pass a unique uuid here so each attendee
+    gets a distinct scannable QR.
+    """
     now = datetime.now(timezone.utc)
+    row_id = ticket_id or payment_hash
 
     # name/email columns are NOT NULL in the schema, so we store "" when only
     # user_id is supplied. _parse_ticket_row reverses this on read.
@@ -54,7 +65,7 @@ async def create_ticket(
         db_email = email or ""
 
     db_ticket = Ticket(
-        id=payment_hash,
+        id=row_id,
         wallet=wallet,
         event=event,
         name=db_name,
@@ -65,11 +76,12 @@ async def create_ticket(
         reg_timestamp=now,
         time=now,
         extra=TicketExtra(**extra) if extra else TicketExtra(),
+        payment_hash=payment_hash,
     )
     await db.insert("events.ticket", db_ticket)
 
     return Ticket(
-        id=payment_hash,
+        id=row_id,
         wallet=wallet,
         event=event,
         name=name,
@@ -80,6 +92,7 @@ async def create_ticket(
         reg_timestamp=now,
         time=now,
         extra=TicketExtra(**extra) if extra else TicketExtra(),
+        payment_hash=payment_hash,
     )
 
 
@@ -93,6 +106,21 @@ async def update_ticket(ticket: Ticket) -> Ticket:
     return ticket
 
 
+async def get_tickets_by_payment_hash(payment_hash: str) -> list[Ticket]:
+    """All ticket rows sharing the given LNbits invoice payment_hash.
+
+    For a single-ticket purchase returns one row (legacy invariant
+    `id == payment_hash` still holds). For a multi-ticket purchase
+    returns the N rows created with shared `payment_hash` but
+    distinct `id`s — each attendee's scannable QR.
+    """
+    rows = await db.fetchall(
+        "SELECT * FROM events.ticket WHERE payment_hash = :ph",
+        {"ph": payment_hash},
+    )
+    return [Ticket(**_parse_ticket_row(row)) for row in rows]
+
+
 async def get_ticket(payment_hash: str) -> Ticket | None:
     row = await db.fetchone(
         "SELECT * FROM events.ticket WHERE id = :id",