buzz-cli: --pubkey flags reject npub while --mention accepts it

[jurgenhaas]

Problem

Every --pubkey flag in buzz-cli validates with validate_hex64 (crates/buzz-cli/src/validate.rs:29), so it only accepts 64-char hex. But messages send --mention normalizes with nostr::PublicKey::parse (crates/buzz-cli/src/commands/messages.rs:231-232), which accepts hex and bech32 npub1….

The result is an inconsistent surface, and it bites during the most common onboarding path: Buzz Desktop and chat both surface an npub, so adding a new member requires a manual bech32 decode before this works:

buzz channels add-member --channel <uuid> --pubkey <64-char-hex> --role member

Passing the npub fails with must be a 64-character hex string: npub1…, and there is no npub↔hex conversion subcommand in the CLI.

Proposal

Add a normalize_pubkey helper that accepts either form and returns lowercase hex, and use it for user-identity flags: channels add-member/remove-member, users get/presence, dms open/add-member, moderation ban/unban/timeout/untimeout, agents archive/unarchive.

Git-protocol pubkey fields (repo owner, patch/PR/issue author and recipient) are copied from CLI output rather than typed by hand, so those can stay hex-only for now.

[nawazish2]

Opened a PR for this: #5174

--pubkey on the identity commands now accepts hex or npub (same path --mention already used).