docs(skills): default post-merge worktree/branch cleanup

- pr-review §7a: after a PR merges, recommend tearing down the worktree
  and deleting the merged topic branch (local + origin) by default —
  state the action, let the user decline; never touch protected branches;
  git branch -d as the unmerged-work safety net.
- whats-next §3c: document the worktree lifecycle — created at activation,
  removed by pr-review §7a at merge; prune stale worktrees before creating.

Closes the gap that left empty worktrees parked at main's HEAD.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

.claude/skills/pr-review/SKILL.md

@@ -312,6 +312,38 @@ tea pr close --login schweitz --repo jpmschweitzer/settled-reach <PR_NUMBER>
 Gitea does **not** auto-close PRs when you push a local merge — always close
 manually with `tea pr close` after pushing.
 
+### 7a. Post-merge cleanup (default — suggest it, don't ask open-ended)
+
+Once a PR is merged and closed, its branch is fully contained in `main` and its
+worktree is idle. **The default is to tear both down** — leaving them around is
+how stale empty worktrees accumulate. So after the merge, *recommend* cleanup as
+the default and proceed unless the user wants to keep them. Don't pose it as an
+open question — state the default action, give the user a chance to decline.
+
+```bash
+# 1. Remove the worktree (if the branch had one)
+WORKTREE=$(git worktree list --porcelain | grep -B2 "branch refs/heads/<branch>" | grep "worktree " | sed 's/worktree //')
+git worktree remove "$WORKTREE"           # add --force only if it has uncommitted junk
+
+# 2. Delete the merged branch — local then origin
+git branch -d <branch>                     # -d (not -D) refuses if not merged: a safety net
+git push origin --delete <branch>
+```
+
+Safety rules:
+- **Never delete protected branches** (`main`, `maintenance`, `server`, `client`,
+  `copy`, `audio`, `visual`, `ci`) — see `tea-cli.md`. Cleanup applies only to
+  topic branches.
+- Use `git branch -d` (lowercase) — it refuses to delete a branch not merged into
+  HEAD, so it can't silently drop unmerged work. If it refuses, the branch isn't
+  actually merged: stop and investigate, don't reach for `-D`.
+- This is safe because the commits live in `main` after the merge — but it is still
+  an outward action (deletes the origin branch). Recommend-and-proceed is fine for a
+  merged topic branch; if anything looks unmerged or shared, ask first.
+
+If `/whats-next` created the worktree (kanban flow), this is the step that closes
+that loop — the worktree it spun up at activation is removed here at merge.
+
 ### 8. Post-review actions
 
 **CHANGES_REQUESTED:**

.claude/skills/whats-next/SKILL.md

@@ -192,6 +192,13 @@ git worktree add "$WORKTREE_DIR" <branch-name>
 
 Report the worktree path so the user can open a terminal there.
 
+**Lifecycle:** a worktree created here is torn down at the *end* of the work, not
+here. `/pr-review` §7a removes it (and deletes the merged branch) by default once
+the PR merges. If you activate a batch and the work never ships, the worktree is
+yours to clean up — don't leave empty worktrees parked at `main`'s HEAD (a sign of
+an abandoned activation). Before creating a new worktree, `git worktree list` and
+reuse or prune any stale one for the same branch.
+
 ### 3d. Spawn implementation agents (optional)
 
 If the user wants agents, spawn them using general-purpose subagent_type