PR #2943 fixed headers in buildHeaders() but the login flow in
waitForLogin() still used a hardcoded incomplete header object.
Reuse the shared buildHeaders() so all endpoints send consistent
iLink-App-Id and iLink-App-ClientVersion headers.
Also wrap channel.connect() in startSingle() with a try/catch so
configuration errors print a clean message instead of dumping the
yargs help text and a stack trace.
The iLink Bot API requires these headers for session authentication.
Without them, getupdates returns errcode -14 (session timeout).
The protocol version (2.0.0) is tracked independently from our channel
version, matching the current official plugin's API compatibility level.
Closes#2908
