Allow hyphenated @mentions such as @telegram-bridge

[realproject7]

Problem

The mention parser currently truncates hyphenated handles. A message containing @telegram-bridge is parsed as @telegram, which produces a false unknown-agent warning even when telegram-bridge is a registered agent.

Current code path observed by the operator uses a regex equivalent to @(\w+), which does not include hyphens.

Repro

1. Send a message containing @telegram-bridge
2. Observe the parser capture telegram instead of telegram-bridge
3. The system emits an unknown-agent warning for @telegram

Expected

Hyphenated handles should be parsed as full registered names.

Acceptance Criteria

• Hyphenated handles such as @telegram-bridge are captured as full mentions
• Valid hyphenated handles no longer emit false unknown-agent warnings
• Exact unknown handles still emit the warning
• Coverage is added or validation is updated for hyphenated handles

Notes

Related orchestration-side tracking: realproject7/agent-os#354 covers the seed-instruction cleanup that contributed to the confusion, but the parser fix itself lives in this repo.