* feat: extract repo parsing into shared util and add linear comment repo override
Moves the repo extraction regex logic (repo:, repo , GitHub URL) into
agent/utils/repo.py so it can be reused. Updates the Linear webhook
handler to check the comment body for a custom repo first, falling back
to the team/project mapping when none is specified.
* chore: document repo extraction util and default org configuration
* feat: add generic DEFAULT_REPO_OWNER/DEFAULT_REPO_NAME env vars replacing Slack-only defaults
* chore: remove deprecated SLACK_REPO_OWNER/NAME env vars from docs
---------
Co-authored-by: open-swe[bot] <open-swe@users.noreply.github.com>
