feat: add NIP-52 Nostr publish + sync of calendar events

Approved events are mirrored to Nostr as NIP-52 calendar events (kind
31922) signed by the wallet owner's pubkey, and incoming kind 31922/31923
events from subscribed relays are synced into the local DB so events
created on other LNbits instances or Nostr clients show up locally.

- m009 stores nostr_event_id + nostr_event_created_at on each event
  (used for replaceable updates and NIP-09 deletes); m011 adds location
  + JSON-encoded categories list (NIP-52 location/`t` tags).
- models: Event/PublicEvent/CreateEvent gain location, categories,
  nostr_event_id, nostr_event_created_at; parse_categories validator
  decodes the JSON column on read.
- nostr/{event,nostr_client}.py: Schnorr signing, websocket relay client,
  and a NostrEvent model (publish-only and subscribe variants).
- nostr_publisher.py: build/sign NIP-52 kind 31922 events and NIP-09
  delete events; publish via the relay client.
- nostr_sync.py: subscribe to kinds 31922/31923, dedupe by nostr_event_id
  / d-tag, upsert Events; auto-approves discovered Nostr events since
  they're already public.
- nostr_hooks.py: thin bridge that views_api handlers call to publish
  or delete a NIP-52 event for a given local event. Lives in its own
  module to keep `from . import nostr_client` out of the view layer
  and avoid the views_api -> publisher import cycle.
- views_api: hooks publish_or_delete_nostr_event into create-on-approved,
  update-when-already-published, cancel (delete), delete (delete), and
  approve (publish).
- __init__.py: 3-task lifespan — wait_for_paid_invoices (upstream),
  NostrClient bootstrap, and the NIP-52 sync loop. Module-level
  nostr_client global is set by the bootstrap and read dynamically by
  publish_or_delete_nostr_event so the import order works regardless of
  whether nostrclient is up at startup.

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

views_api.py

@@ -55,6 +55,7 @@ from .models import (
     Ticket,
     TicketPaymentRequest,
 )
+from .nostr_hooks import publish_or_delete_nostr_event
 from .services import refund_tickets
 from .tasks import deregister_payment_listener, register_payment_listener
 
@@ -187,7 +188,12 @@ async def api_event_create(
     if not is_admin and not ext_settings.auto_approve:
         data.status = "proposed"
 
-    return await create_event(data)
+    event = await create_event(data)
+
+    if event.status == "approved":
+        await publish_or_delete_nostr_event(event)
+
+    return event
 
 
 @events_api_router.put("/{event_id}")
@@ -207,7 +213,13 @@ async def api_event_update(
         )
     for k, v in data.dict().items():
         setattr(event, k, v)
-    return await update_event(event)
+    event = await update_event(event)
+
+    # Re-publish the replaceable NIP-52 event if we already announced it.
+    if event.status == "approved" and event.nostr_event_id:
+        await publish_or_delete_nostr_event(event)
+
+    return event
 
 
 @events_api_router.put("/{event_id}/cancel")
@@ -225,6 +237,10 @@ async def api_event_cancel(
     event.canceled = True
     event = await update_event(event)
     await refund_tickets(event.id)
+
+    if event.nostr_event_id:
+        await publish_or_delete_nostr_event(event, delete=True)
+
     return event
 
 
@@ -239,6 +255,10 @@ async def api_form_delete(
         )
     if event.wallet != wallet.wallet.id:
         raise HTTPException(status_code=HTTPStatus.FORBIDDEN, detail="Not your event.")
+
+    if event.nostr_event_id:
+        await publish_or_delete_nostr_event(event, delete=True)
+
     await delete_event(event_id)
     await delete_event_tickets(event_id)
 
@@ -259,7 +279,9 @@ async def api_event_approve(
             detail=f"Event is already {event.status}.",
         )
     event.status = "approved"
-    return await update_event(event)
+    event = await update_event(event)
+    await publish_or_delete_nostr_event(event)
+    return event
 
 
 @events_api_router.put("/{event_id}/reject")