feat: relay publish + availability subscription via nostrclient (#2)

Wire the Nostr layer through the nostrclient extension's relay manager
in-process (spirekeeper pattern), replacing the sketch stubs:

- _sign_and_publish: sign as operator (resolve_signer), optional NIP-44
  encrypt, publish via nostr_client.relay_manager.publish_message. Soft-
  fails (logs, returns None) if no operator onboarded, nostrclient absent,
  or signer can't encrypt — never crashes the booking flow.
- publish_listing (30402) + publish_block_calendar (31923): public, work
  today (sign_event only).
- publish_reservation (30078): NIP-44 encrypted to guest; soft-fails on a
  LocalSigner until a bunker/server-signing signer lands (lnbits#18).
- subscribe_inbound: permanent task answering kind:22000 availability
  queries with kind:22001 (plaintext — availability is public info), the
  client-agnostic availability path parallel to the RPC.

events.py: drop the _plaintext scaffolding (service.py encrypts content in
place) and a broken {operator_pubkey} calendar tag.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_019VUQCfdqiLSsFS2jcGnaFD

nostr/events.py

@@ -67,13 +67,13 @@ def build_reservation_event(booking: Booking, guest_pubkey: str) -> dict:
     }
     return {
         "kind": KIND_RESERVATION,
-        # placeholder — service.py replaces with NIP-44(payload) for guest
+        # plaintext JSON; service.py NIP-44-encrypts this to the guest before
+        # signing (publish_reservation passes encrypt_to=guest_pubkey).
         "content": json.dumps(payload),
         "tags": [
             ["d", booking.id],
             ["p", guest_pubkey],
         ],
-        "_plaintext": payload,  # consumed + stripped by service.py before signing
     }
 
 
@@ -91,7 +91,6 @@ def build_block_calendar_event(
             ["title", f"{room.title} — unavailable"],
             ["start", start_date],
             ["end", end_date],
-            ["a", f"{KIND_LISTING}:{{operator_pubkey}}:{room.id}"],  # link to listing
         ],
     }
 
@@ -99,8 +98,13 @@ def build_block_calendar_event(
 def build_availability_response(
     result: AvailabilityResult, requester_pubkey: str
 ) -> dict:
-    """Aiolabs kind:22001 (ephemeral) reply to an availability query. Content
-    MUST be NIP-44 encrypted to the requester by service.py."""
+    """Aiolabs kind:22001 (ephemeral) reply to an availability query.
+
+    Plaintext by design: room availability for a date range is public
+    information (the same facts published in the NIP-52 calendar), so this
+    needs no encryption — which also means it works today without a bunker/
+    server-signing signer (only sign_event is required, not nip44_encrypt).
+    p-tagged to the requester so their client can match the reply."""
     payload = {
         "room_id": result.room_id,
         "check_in": result.check_in,
@@ -115,5 +119,4 @@ def build_availability_response(
         "kind": KIND_AVAILABILITY_RESPONSE,
         "content": json.dumps(payload),
         "tags": [["p", requester_pubkey]],
-        "_plaintext": payload,
     }