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>

nostr_hooks.py

@@ -0,0 +1,43 @@
+"""Helpers that bridge event-mutation handlers to the Nostr publisher.
+
+Lives in its own module so both `events_api_router` and any future router
+can call it without importing through `views_api`, which would create an
+import cycle (views_api -> nostr_hooks -> nostr_publisher -> models).
+"""
+
+from loguru import logger
+
+from .crud import update_event
+from .models import Event
+from .nostr_publisher import publish_event_to_nostr
+
+
+async def publish_or_delete_nostr_event(event: Event, *, delete: bool = False) -> None:
+    """Publish or delete the NIP-52 calendar event for `event`.
+
+    Pulls the wallet owner's pubkey/prvkey to sign with the user's identity.
+    Failures are logged and swallowed so a Nostr outage doesn't break the
+    HTTP flow that triggered the publish.
+    """
+    try:
+        from lnbits.core.crud.users import get_account
+        from lnbits.core.crud.wallets import get_wallet
+
+        from . import nostr_client
+
+        wallet_obj = await get_wallet(event.wallet)
+        if not wallet_obj:
+            return
+        account = await get_account(wallet_obj.user)
+        if not account or not account.pubkey or not account.prvkey:
+            return
+
+        nostr_event = await publish_event_to_nostr(
+            nostr_client, event, account.pubkey, account.prvkey, delete=delete
+        )
+        if nostr_event and not delete:
+            event.nostr_event_id = nostr_event.id
+            event.nostr_event_created_at = nostr_event.created_at
+            await update_event(event)
+    except Exception as exc:
+        logger.warning(f"[EVENTS] Nostr publish failed: {exc}")