ultrareview can now review a repo's very first commit

What

• When the current branch's only commit is the repo's very first commit, ultrareview no longer silently falls back to diffing against an empty tree; it can offer to review every file in that first commit, but only after confirmation.
• Confirmation is skipped when the launch comes from certain internal request paths (flagged confirmsBeforeLaunch), or when a person invoked the review command directly.
• Review-scope messaging gained a dedicated "first commit" case, with a companion error message explaining that a fresh repo needs at least one commit before review can work, instead of falling through to a generic "no merge base" message.
• The remote-review precondition check's error message now says the argument can be a commit as well as a branch name, and a new bundling helper accepts a first-commit-only flag with a matching first_commit telemetry field recorded when a diff is too large to review.

Why

Previously, reviewing a brand-new repo with only its initial commit either failed or produced a confusing empty-diff review. Now Claude Code recognizes this case, explains it clearly, and can review the whole first commit with proper confirmation.