fix(pairing): default relay to the transport's nostrrelay, not nostrclient proxy

The nostrclient endpoint is a subscription MULTIPLEXER, not a full relay: its
router forwards a client's EVENT upstream but never returns an OK ack (see
nostrclient/router.py). A transport client that awaits OK on publish therefore
times out ("publish timed out"), so kind-21000 RPCs never complete — verified
on the Sintra: connect succeeded but list_wallets hung, and switching to the
nostrrelay endpoint made the whole flow work (wallet, balance, availability).

default_relay_endpoint now derives from settings.nostr_transport_relays — the
relay the transport actually listens on: use it as-is when already
machine-reachable, or re-home its path on lnbits_baseurl when it's a co-located
loopback relay (the bundled nostrrelay). Validation/localhost-reject and the
pair-dialog pre-fill/hint carry over; wording updated to "transport relay".

227 tests pass.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

tests/test_pairing.py

@@ -35,7 +35,9 @@ from ..pairing import (
 )
 
 _BASEURL = "https://lnbits.example.com/"
-_NOSTRCLIENT_ENDPOINT = "wss://lnbits.example.com/nostrclient/api/v1/relay"
+_TRANSPORT_RELAY = "ws://localhost:5001/nostrrelay/test"
+# baseurl host (wss://lnbits.example.com) + transport relay path (/nostrrelay/test)
+_DEFAULT_RELAY = "wss://lnbits.example.com/nostrrelay/test"
 
 _NOW = datetime(2026, 6, 16, tzinfo=timezone.utc)
 _SPIRE_HEX = "522a4538f1df96508d9ee8b14072344dd4a566acfe03c25a92a39179c6fca891"
@@ -53,11 +55,14 @@ def _set_transport_pubkey():
     # lnbits_npub in the seed (bitspire#70). Set it for every test; restore after.
     prev = settings.nostr_transport_public_key
     prev_base = settings.lnbits_baseurl
+    prev_relays = settings.nostr_transport_relays
     settings.nostr_transport_public_key = _LNBITS_HEX
     settings.lnbits_baseurl = _BASEURL
+    settings.nostr_transport_relays = [_TRANSPORT_RELAY]
     yield
     settings.nostr_transport_public_key = prev
     settings.lnbits_baseurl = prev_base
+    settings.nostr_transport_relays = prev_relays
 
 
 @pytest.fixture(autouse=True)
@@ -327,8 +332,8 @@ def test_missing_passphrase_raises():
         )
 
 
-def test_relays_default_to_nostrclient_endpoint():
-    # No relays given → derived from lnbits_baseurl → nostrclient proxy endpoint.
+def test_relays_default_to_transport_relay():
+    # No relays given → derived from the transport relay, re-homed on baseurl.
     result = asyncio.run(
         pair_spire(
             _machine(),
@@ -336,34 +341,51 @@ def test_relays_default_to_nostrclient_endpoint():
             keystore_passphrase=_PASSPHRASE,
         )
     )
-    assert _decode_seed(result.seed_url)["relays"] == [_NOSTRCLIENT_ENDPOINT]
+    assert _decode_seed(result.seed_url)["relays"] == [_DEFAULT_RELAY]
 
 
-def test_default_relay_endpoint_scheme_map():
-    prev = settings.lnbits_baseurl
+def test_default_relay_endpoint_rehomes_loopback_transport_relay():
+    prev_base = settings.lnbits_baseurl
+    prev_relays = settings.nostr_transport_relays
     try:
+        # loopback transport relay → re-homed on the base URL host
+        settings.nostr_transport_relays = ["ws://localhost:5001/nostrrelay/test"]
         settings.lnbits_baseurl = "http://192.168.0.32:5001"
-        assert default_relay_endpoint() == "ws://192.168.0.32:5001/nostrclient/api/v1/relay"
+        assert default_relay_endpoint() == "ws://192.168.0.32:5001/nostrrelay/test"
         settings.lnbits_baseurl = "https://lnbits.example.com/"
-        assert default_relay_endpoint() == _NOSTRCLIENT_ENDPOINT
+        assert default_relay_endpoint() == _DEFAULT_RELAY
+        # loopback relay but no base URL → can't re-home → None
         settings.lnbits_baseurl = ""
         assert default_relay_endpoint() is None
     finally:
-        settings.lnbits_baseurl = prev
+        settings.lnbits_baseurl = prev_base
+        settings.nostr_transport_relays = prev_relays
 
 
-def test_no_relays_and_no_baseurl_raises():
-    prev = settings.lnbits_baseurl
+def test_default_relay_endpoint_passes_through_reachable_transport_relay():
+    prev = settings.nostr_transport_relays
     try:
-        settings.lnbits_baseurl = ""
-        with pytest.raises(PairingError, match="cannot derive"):
+        # already remote-reachable → used as-is, base URL irrelevant
+        settings.nostr_transport_relays = ["wss://relay.aiolabs.dev"]
+        assert default_relay_endpoint() == "wss://relay.aiolabs.dev"
+        settings.nostr_transport_relays = []
+        assert default_relay_endpoint() is None
+    finally:
+        settings.nostr_transport_relays = prev
+
+
+def test_no_relays_and_no_transport_relay_raises():
+    prev = settings.nostr_transport_relays
+    try:
+        settings.nostr_transport_relays = []
+        with pytest.raises(PairingError, match="none could be derived"):
             asyncio.run(
                 pair_spire(
                     _machine(), admin_client=FakeBunker(), keystore_passphrase=_PASSPHRASE
                 )
             )
     finally:
-        settings.lnbits_baseurl = prev
+        settings.nostr_transport_relays = prev
 
 
 @pytest.mark.parametrize(