feat(nostr): NIP-99 menu listings, NIP-01 profile, NIP-17 stub

nostr/event.py
  Bare NIP-01 NostrEvent with canonical id computation.

nostr/nostr_client.py
  Bidirectional WebSocket client (lifted from events ext, kept
  local). Connects to nostrclient ext's internal relay endpoint,
  dedups by event id (LRU 1000).

nostr_publisher.py
  Builders for:
    * kind 0    — restaurant profile (NIP-01 metadata)
    * kind 30402 — menu item (NIP-99 classified listing,
                              parameterized replaceable by item.id)
    * kind 5    — deletion request (NIP-09)
  Schnorr signing via coincurve (BIP-340).

  Menu listings carry structured price tags (["price", n, currency]),
  status (active|sold) so customers see sold-out items, and 't' tags
  for category, dietary, allergens (allergen:<x>) and ingredients
  (ingr:<x>) so webapps can filter without parsing markdown.

  Restaurants can sign with their own keypair (per-restaurant Nostr
  identity) or fall back to the LNbits Account keypair.

nostr_sync.py
  Subscribes to:
    * kind 30402 #t=menu — backfill 200 + live (echo confirmation
      for now; foreign-menu indexing deferred until we settle on a
      federated cache table).
    * kind 1059 — NIP-17 gift-wrapped DMs, only when
      settings.nostr_orders_enabled. Decryption stubbed (needs
      NIP-44 v2 unwrap); REST stays the supported transport
      until that's wired up. _place_order_from_dm is complete and
      ready for the decryption hook.

nostr/event.py

@@ -0,0 +1,36 @@
+"""
+Bare NIP-01 event model.
+
+Same shape as the events extension; kept independent so the two
+extensions can evolve their Nostr payloads without coupling.
+"""
+
+import hashlib
+import json
+from typing import List, Optional
+
+from pydantic import BaseModel
+
+
+class NostrEvent(BaseModel):
+    id: str = ""
+    pubkey: str
+    created_at: int
+    kind: int
+    tags: List[List[str]] = []
+    content: str = ""
+    sig: Optional[str] = None
+
+    def serialize(self) -> List:
+        # Per NIP-01, the canonical event id is sha256 of:
+        #   [0, pubkey, created_at, kind, tags, content]
+        return [0, self.pubkey, self.created_at, self.kind, self.tags, self.content]
+
+    def serialize_json(self) -> str:
+        return json.dumps(
+            self.serialize(), separators=(",", ":"), ensure_ascii=False
+        )
+
+    @property
+    def event_id(self) -> str:
+        return hashlib.sha256(self.serialize_json().encode()).hexdigest()