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/channels/adapter.ts

@@ -60,6 +60,21 @@ export interface InboundMessage {
   kind: 'chat' | 'chat-sdk';
   content: unknown; // JS object — host will JSON.stringify before writing to session DB
   timestamp: string;
+  /**
+   * Platform-confirmed signal that this message is a mention of the bot.
+   *
+   * Set by adapters that know the platform's own mention semantics — e.g.
+   * the Chat SDK bridge sets it true from `onNewMention` / `onDirectMessage`
+   * and forwards `message.isMention` from `onSubscribedMessage`. Use this
+   * in the router instead of agent-name regex matching, which breaks on
+   * platforms where the mention text is the bot's platform username (e.g.
+   * Telegram's `@nanoclaw_v2_refactr_1_bot`) rather than the agent_group
+   * display name (e.g. `@Andy`).
+   *
+   * Adapters that don't set it (native / legacy) leave it undefined — the
+   * router falls back to text-match against agent_group_name.
+   */
+  isMention?: boolean;
 }
 
 /** A file attachment to deliver alongside a message. */