buzz channels add-member fails

Describe the bug
buzz channels add-member --channel --pubkey fails with relay error 400: invalid: missing p tag. The NIP-28 kind 43 event generated by the CLI is missing the required p tag that identifies the member being added. Without the p tag, the relay rejects the event as invalid.

Steps to reproduce
1. Create a channel: buzz channels create --name "Test" --type stream --visibility private
2. Note the returned channel_id
3. Attempt to add a member: buzz channels add-member --channel --pubkey <64-char-hex-pubkey> --role admin
4. See error: {"error":"relay_error","message":"relay error 400: invalid: missing p tag","retryable":false}

Expected behavior
The CLI should include the --pubkey value as a p tag in the NIP-28 kind 43 event. The relay should accept the event and add the member to the channel.

Version and platform
- Buzz version: unknown (installed at /usr/bin/buzz)
- OS: Linux (Pop!_OS)

Logs / additional context

$ BUZZ_PRIVATE_KEY= BUZZ_RELAY_URL=wss://livingwatersict.communities.buzz.xyz /usr/bin/buzz channels add-member --channel e2dbe418-2412-4fee-a99d-8a60abb203aa --pubkey 5d5360fffb18844011d6ae4d812eab926897be58376f801541b40aeb4c54b0ea --role admin
{"error":"relay_error","message":"relay error 400: invalid: missing p tag","retryable":false}

Same error occurs without --role admin. The channel was successfully created moments before, confirming the relay is reachable and the key is valid.