fix(connector): stop first-come /link owner takeover across chat adapters

[DHDHLZ]

Security fix: messaging adapters bound the FIRST caller of /link as owner
when none was configured (Telegram, Discord, Slack, Feishu all shared the
same first-come logic).

Impact: bots are publicly reachable, so during the unlinked setup window
whoever messages /link first becomes the owner and inherits every
owner-gated surface (inbox, desk issues, and the UTA review/push actions).

Change:

• /link now only binds a chat for the owner that is pre-configured in
  Connector settings (ownerUserId).
• An unconfigured connector refuses to bind and explains the requirement,
  so there is no anonymous first-come path.

Tests:

• new owner-link-guard.spec.ts: refuse-when-unconfigured, bind-for-
  configured-owner, reject-non-owner (36 connector adapter tests pass);
• feishu.spec.ts updated from the old first-bind contract to the
  configured-owner contract;
• npx tsc --noEmit passes.

[vercel]

@DHDHLZ is attempting to deploy a commit to the luokerenx4's Team Team on Vercel.

A member of the Team first needs to authorize it.