fix: Date/Message-ID/From-name on ticket emails, richer body (1.6.1-aio.9)

A tester's ticket email landed in spam. A mail-tester run against demo
scored 8.3/10 with SPF, DKIM and DMARC all passing through the VPS relay,
so the deductions were all in the message: MISSING_DATE (1.4),
HTML_IMAGE_ONLY_04 (0.3), MISSING_MID (0.1) — and Gmail/Outlook weigh a
missing Date/Message-ID as "machine-generated" far more than that.

- `build_ticket_email` sets Date, a Message-ID under the sender domain,
  and a From display name from `lnbits_site_title`.
- The body now carries the event name, dates, location, name on ticket,
  ticket id and the door instruction, so the HTML part is no longer a
  QR with a handful of words.

Upstream candidate: lnbits core `send_email` has the same omissions.

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

tests/test_ticket_email.py

@@ -0,0 +1,69 @@
+from datetime import datetime, timezone
+
+from lnbits.settings import settings
+
+from ..models import Event, Ticket
+from ..services import _ticket_notification_payload, build_ticket_email
+
+
+def _event(**overrides) -> Event:
+    data = {
+        "id": "evt1",
+        "wallet": "w",
+        "name": "Test Event",
+        "info": "",
+        "closing_date": "2030-01-01",
+        "event_start_date": "2030-01-01T16:00:00+01:00",
+        "event_end_date": "2030-01-01T20:00:00+01:00",
+        "location": "The Chateau",
+        "amount_tickets": 10,
+        "price_per_ticket": 5,
+        "time": datetime.now(timezone.utc),
+    }
+    data.update(overrides)
+    return Event(**data)
+
+
+def _ticket(**overrides) -> Ticket:
+    now = datetime.now(timezone.utc)
+    data = {
+        "id": "tkt1",
+        "wallet": "w",
+        "event": "evt1",
+        "name": "Ada",
+        "email": "ada@example.com",
+        "registered": False,
+        "paid": True,
+        "time": now,
+        "reg_timestamp": now,
+    }
+    data.update(overrides)
+    return Ticket(**data)
+
+
+def test_email_carries_date_message_id_and_display_name(monkeypatch):
+    monkeypatch.setattr(settings, "lnbits_site_title", "Oyez!")
+    msg = build_ticket_email(
+        "tickets@example.org", ["ada@example.com"], "Subj", "text", "<p>html</p>"
+    )
+    assert msg["Date"]
+    assert msg["Message-ID"].endswith("@example.org>")
+    assert msg["From"] == "Oyez! <tickets@example.org>"
+    parts = [p.get_content_type() for p in msg.get_payload()]
+    assert parts == ["text/plain", "text/html"]
+
+
+def test_payload_includes_event_details_and_qr(monkeypatch):
+    monkeypatch.setattr(settings, "lnbits_baseurl", "https://lnbits.example/")
+    subject, text, html = _ticket_notification_payload(_ticket(), _event())
+    assert "Test Event" in subject
+    for needle in (
+        "Event: Test Event",
+        "Where: The Chateau",
+        "Name on ticket: Ada",
+        "Ticket ID: tkt1",
+        "at the door",
+    ):
+        assert needle in text
+    assert "/events/api/v1/qr/tkt1" in text
+    assert "<img" in html and "Ticket ID: tkt1" in html