system_append.md and system_append_pr_review.md hardcoded the literal
'robomp' as the bot persona, so the agent self-mentioned an account
that does not exist when deployments configure ROBOMP_BOT_LOGIN to a
different login. Affected users saw the agent ask for @robomp mentions
that GitHub never resolved to the actual bot.
Thread the configured login through persona.system_append and
persona.system_append_pr_review as a bot_login keyword, render it
via the existing {{bot_login}} placeholder, and pass
settings.bot_login at the worker callsite. Regression test asserts the
templated login lands in both prompts and the legacy literal is gone.
Fixes#1932
roboomp
ae89b68b90