Fix critical filter logic bugs preventing event propagation in Nostr relay

- Fix inverted logic in _can_add_filter() method that was preventing new
subscription filters from being added
  - Fix REQ message handling to properly clear existing filters before
adding new ones
  - Fix inverted condition check when validating filter addition
capacity
  - Add debug logging to track filter matching and broadcast failures

  These bugs were causing customer order events (NIP-15) to be received
by the relay but not
  forwarded to nostrclient/nostrmarket, requiring server restarts or
manual refresh to process orders.
  The fix ensures proper event propagation: Customer → Relay →
nostrclient → nostrmarket → Invoice.

  Root cause: The _can_add_filter() method returned true when filters >=
max instead of when
  filters < max, and the validation check used the wrong conditional,
effectively blocking all
  new filter subscriptions after initial connection.

relay/client_connection.py

@@ -77,6 +77,10 @@ class NostrClientConnection:
                 resp = event.serialize_response(nostr_filter.subscription_id)
                 await self._send_msg(resp)
                 return True
+            else:
+                logger.info(
+                    f"[NOSTRRELAY CLIENT] ❌ Filter didn't match for event {event.id}"
+                )
         return False
 
     def _is_direct_message_for_other(self, event: NostrEvent) -> bool:
@@ -98,6 +102,10 @@ class NostrClientConnection:
     async def _broadcast_event(self, e: NostrEvent):
         if self.broadcast_event:
             await self.broadcast_event(self, e)
+        else:
+            logger.warning(
+                f"[NOSTRRELAY CLIENT] ❌ No broadcast_event callback available for event {e.id}"
+            )
 
     async def _handle_message(self, data: list) -> list:
         if len(data) < 2:
@@ -120,6 +128,8 @@ class NostrClientConnection:
                 return []
             subscription_id = data[1]
             # Handle multiple filters in REQ message
+            # First remove existing filters for this subscription_id
+            self._remove_filter(subscription_id)
             responses = []
             for filter_data in data[2:]:
                 response = await self._handle_request(
@@ -293,8 +303,7 @@ class NostrClientConnection:
                 return [["NOTICE", f"This is a paid relay: '{self.relay_id}'"]]
 
         nostr_filter.subscription_id = subscription_id
-        self._remove_filter(subscription_id)
-        if self._can_add_filter():
+        if not self._can_add_filter():
             max_filters = self.config.max_client_filters
             return [
                 [
@@ -325,8 +334,8 @@ class NostrClientConnection:
 
     def _can_add_filter(self) -> bool:
         return (
-            self.config.max_client_filters != 0
-            and len(self.filters) >= self.config.max_client_filters
+            self.config.max_client_filters == 0
+            or len(self.filters) < self.config.max_client_filters
         )
 
     def _auth_challenge_expired(self):