fix(router): trust SDK isMention signal; drop broken hasMention regex

The router's mention / mention-sticky engage check was regex-matching
@<agent_group.name> (e.g. @Andy) against message text. Platforms don't
work that way — users address bots via the bot's platform username
(@nanoclaw_v2_refactr_1_bot on Telegram, user-id mentions on Slack /
Discord). The regex matched only coincidentally and never on Telegram,
so mention-mode wirings silently never fired there.

Two parallel mention detectors existed: the Chat SDK's onNewMention,
which correctly resolves the bot's platform identity, and the router's
hasMention text regex, which ignored the SDK verdict and invented its
own heuristic. The router's detector was wrong in principle — the agent
group's display name is a NanoClaw-side nickname, not a platform
address.

Thread the SDK signal through: InboundMessage gains an optional
`isMention` field, the bridge sets it from each handler (onNewMention →
true, onDirectMessage → true, onSubscribedMessage → message.isMention,
onNewMessage(/./) → false), src/index.ts forwards it into InboundEvent,
and evaluateEngage now checks `isMention === true` for mention modes.
hasMention deleted entirely — there is only one source of truth for
"did the user mention this bot": the platform / SDK.

Agent-name-in-text matching for disambiguating multiple agents wired to
one chat is a separate feature; users can express it today with
engage_mode='pattern' + the agent's name as the regex.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

src/index.ts

@@ -83,6 +83,7 @@ async function main(): Promise<void> {
             kind: message.kind,
             content: JSON.stringify(message.content),
             timestamp: message.timestamp,
+            isMention: message.isMention,
           },
         }).catch((err) => {
           log.error('Failed to route inbound message', { channelType: adapter.channelType, err });