feat(polecat): self-cleaning model and new review formulas

Polecats now self-clean when done:
- gt done always exits session (no more --exit flag needed)
- gt done requests self-nuke (sandbox cleanup)
- No idle polecats - done means gone
- Refinery re-implements on conflict (never sends work back)

New formulas:
- mol-polecat-review-pr: review external PRs, approve/reject
- mol-polecat-code-review: review code, file beads for findings

Docs updated:
- polecat-lifecycle.md: self-cleaning model, identity vs session
- polecat-CLAUDE.md: updated contract and completion protocol
- mol-polecat-work: updated for self-cleaning

Implementation beads filed:
- gt-yrz4k: gt done always exits
- gt-fqcst: polecat self-nuke mechanism
- gt-zdmde: abstract work unit completion

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

templates/polecat-CLAUDE.md

@@ -46,8 +46,16 @@ pinned molecule (steps poured from `mol-polecat-work`) and signal completion to
 You:
 1. Receive work via your hook (pinned molecule + issue)
 2. Work through molecule steps using `bd ready` / `bd close <step>`
-3. Signal completion and exit (`gt done --exit`)
-4. Witness handles cleanup, Refinery merges
+3. Complete and self-clean (`gt done`) - you exit AND nuke yourself
+4. Refinery merges your work from the MQ
+
+**Self-cleaning model:** When you run `gt done`, you:
+- Push your branch to origin
+- Submit work to the merge queue
+- Nuke your own sandbox and session
+- Exit immediately
+
+There is no idle state. Done means gone.
 
 **Important:** Your molecule already has step beads. Use `bd ready` to find them.
 Do NOT read formula files directly - formulas are templates, not instructions.
@@ -150,17 +158,18 @@ When your work is done, follow this EXACT checklist:
 [ ] 1. Tests pass:        go test ./...
 [ ] 2. Commit changes:    git add <files> && git commit -m "msg (issue-id)"
 [ ] 3. Sync beads:        bd sync
-[ ] 4. Exit session:      gt done --exit
+[ ] 4. Self-clean:        gt done
 ```
 
-**Note**: No push needed - your branch stays local. Refinery accesses it
-via shared .repo.git and merges to main.
+The `gt done` command (self-cleaning):
+- Pushes your branch to origin
+- Creates a merge request bead in the MQ
+- Nukes your sandbox (worktree cleanup)
+- Exits your session immediately
 
-The `gt done --exit` command:
-- Creates a merge request bead
-- Notifies the Witness
-- Exits your session immediately (no idle waiting)
-- Witness handles cleanup, Refinery merges your branch
+**You are gone after `gt done`.** No idle waiting. The Refinery will merge
+your work from the MQ. If conflicts arise, a fresh polecat re-implements -
+work is never sent back to you (you don't exist anymore).
 
 ### No PRs in Maintainer Repos