Add Pi review-runner adapter; drop `entire review attach`

Pi can now be driven by entire review like claude-code/codex/gemini: it runs headless via pi --mode json <prompt>, inherits the ENTIRE_REVIEW_* env vars, and self-tags its session through the existing hook adoption path. No marker file or manual attach is needed.

• Add cmd/entire/cli/agent/pi/reviewer.go: NewReviewer() (ReviewerTemplate)
  • a parser mapping pi's JSON event stream to review Events, with tests.
• Wire pi into launchableReviewerFor.
• Remove the entire review attach subcommand and its plumbing (Deps.AttachCmd, newReviewAttachCmd). Its only unique behavior — consuming a pending-review marker — is folded into entire attach --review, which already covers manual tagging. Tests migrated to the attach --review surface; stale doc comments updated.