Address only the longer of two @names in a group, and not a Bot named by an email address

[Chebaleomkar]

What this changes

mentionedPeers in server/src/channels/group.ts matched each Bot's @name on its own:

• With Bots "Ops" and "Ops Lead", @Ops Lead please look returned both, because "Ops" followed by a space passes the lookahead. In send both Bots answered. In relay the unintended Bot got a queued turn, an audit row and a fan-out slot.
• Nothing was required before the @, so write to jo@sam.com addressed a Bot called Sam.

Now an @ straight after a letter, digit or _ is not a mention, and where two names match at the same @, only the longer one counts. The speaker is still matched, so its own longer name hides a shorter peer's, and it is still never returned.

Where it runs

Server: group conversations, both a person's message (send) and Bot-to-Bot relays.

Boundary and audit

Fewer unintended relays, so fewer unintended mayAddress checks and audit rows. Depth and fan-out checks are unchanged.

Changelog

Entry under Unreleased.

Proof

New test in server/tests/group-conversations.test.ts. It fails on main (3 pass, 1 fail) and passes with the fix (4/4). Server tsc and Biome format and lint are clean.