[Fix] Reuse add naming for PR worktrees

[samzong]

What's changed?

• Reuse the standard worktree add path and branch naming for PR worktrees.
• Create PR branches as pr/ while preserving sanitized worktree directory names.
• Add coverage for PR worktree creation in bare-layout and normal repositories.
• Address lint findings in formatter rename parsing and LLM version prompt construction.

Why

• Keeps PR worktree behavior consistent with regular worktree add behavior and restores the full make check gate.