feat(pairing-ui): pre-fill the pair dialog relay with the default endpoint

The backend now defaults an omitted relay to the nostrclient proxy endpoint,
but the pair dialog still showed an empty, client-side-required field — so the
operator saw "no default". Wire it through:

- GET /api/v1/dca/default-relay returns default_relay_endpoint() (the derived
  ws(s)://<host>/nostrclient/api/v1/relay).
- openPairDialog pre-fills the relay textarea with it; the operator can override
  or clear it (blank → same server-side default). Drops the client-side
  "at least one relay is required" guard.
- Hint updated to explain the default.

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

static/js/index.js

@@ -839,12 +839,21 @@ window.app = Vue.createApp({
     // -----------------------------------------------------------------
     // Pair / revoke spire (S0 / #9, #12)
     // -----------------------------------------------------------------
-    openPairDialog(machine) {
+    async openPairDialog(machine) {
       this.pairDialog.machine = machine
       this.pairDialog.relays = ''
       this.pairDialog.durationHours = null
       this.pairDialog.result = null
       this.pairDialog.show = true
+      // Pre-fill with this lnbits' default relay (the nostrclient proxy
+      // endpoint derived from lnbits_baseurl). The operator can override or
+      // clear it; if left blank the backend fills in the same default.
+      try {
+        const {data} = await LNbits.api.request('GET', `${API}/default-relay`)
+        if (data && data.relay) this.pairDialog.relays = data.relay
+      } catch (e) {
+        // Non-fatal: leave blank; the backend still defaults on submit.
+      }
     },
 
     async submitPair() {
@@ -852,14 +861,12 @@ window.app = Vue.createApp({
         .split(/[\s,]+/)
         .map(s => s.trim())
         .filter(Boolean)
-      if (!relays.length) {
-        Quasar.Notify.create({
-          type: 'negative',
-          message: 'At least one relay is required'
-        })
-        return
+      // relays is optional — blank falls back to the nostrclient endpoint
+      // server-side (the pre-filled default), so no client-side requirement.
+      const body = {}
+      if (relays.length) {
+        body.relays = relays
       }
-      const body = {relays}
       if (this.pairDialog.durationHours) {
         body.duration_hours = Number(this.pairDialog.durationHours)
       }

templates/spirekeeper/index.html

@@ -868,7 +868,7 @@
           <q-input
             v-model="pairDialog.relays"
             label="Relay(s) for the spire's events"
-            hint="One per line. The same relay the spire publishes to (its VITE_RELAY_URL), e.g. wss://your-host/nostrrelay/<id>"
+            hint="Pre-filled with this instance's nostrclient relay endpoint (derived from your Base URL). Leave as-is unless the spire must use a different relay. One per line; blank uses the default."
             type="textarea" autogrow
             class="q-mb-md"
             dense outlined></q-input>

tests/test_pair_endpoint.py

@@ -175,3 +175,15 @@ def test_revoke_failure_maps_to_bad_gateway(monkeypatch):
         _call_revoke()
     assert ei.value.status_code == 502
     assert state["unpaired"] is None  # not persisted on failure
+
+
+def test_default_relay_endpoint_returns_nostrclient_url():
+    from lnbits.settings import settings
+
+    prev = settings.lnbits_baseurl
+    try:
+        settings.lnbits_baseurl = "https://lnbits.example.com/"
+        result = asyncio.run(views_api.api_default_relay(SimpleNamespace(id="op1")))
+        assert result == {"relay": "wss://lnbits.example.com/nostrclient/api/v1/relay"}
+    finally:
+        settings.lnbits_baseurl = prev

views_api.py

@@ -33,6 +33,7 @@ from .pairing import (
     PairResult,
     PairingError,
     RevokeResult,
+    default_relay_endpoint,
     pair_spire,
     revoke_spire,
 )
@@ -297,6 +298,16 @@ async def api_create_machine(
     return machine
 
 
+@spirekeeper_api_router.get("/api/v1/dca/default-relay")
+async def api_default_relay(user: User = Depends(check_user_exists)) -> dict:
+    """The relay a pairing seed defaults to when the operator leaves it blank —
+    this lnbits' nostrclient proxy endpoint, derived from lnbits_baseurl
+    (bitspire#70). The pair dialog pre-fills it. `None` if lnbits_baseurl is
+    unset."""
+    _ = user
+    return {"relay": default_relay_endpoint()}
+
+
 @spirekeeper_api_router.post(
     "/api/v1/dca/machines/{machine_id}/pair", response_model=PairResult
 )