[Feature Request] Client and CLI auto-expansion of @everyone / @channel group mentions

[LesleyMurfin]

Summary

Currently in Buzz, sending a message that notifies participants requires explicitly adding a @Full Name or --mention <pubkey> for each individual member. Un-tagged messages in channels are posted passively to the feed without sending notifications or routing events to agents.

Problem

When users want to notify all members in a channel (or trigger all channel-assigned agents to participate in a discussion), they must manually tag each member individually. As channel size grows or team membership changes, this becomes unscalable and easy to miss participants.

Proposed Solution

1. Client/CLI Auto-expansion: Add support in buzz-cli (and Buzz Desktop) to parse @everyone or @channel tokens in message content, auto-resolve all current member pubkeys for the target channel via channel membership metadata, and append explicit Nostr p tags (--mention) to the event before signing and broadcasting.
2. Channel Broadcast Event Tag (Optional Protocol Extension): Define a standard channel-wide mention mechanism or tag convention for channel events.

Value

Allows seamless team-wide announcements and multi-agent discussion triggers across channels without requiring manual per-member tagging.