- `down()` scopes cleanup to a single stack via `app.kubernetes.io/stack` and keeps the namespace `Active` by default
- New `stop/down --delete-namespace` flag for opt-in full teardown
- `down()` is synchronous - waits until resources are actually gone before returning. Callers can drop their own wait loops
- `up()` skip-if-exists for Jobs completes the create-or-replace coverage (other kinds already had it)
- Orphan PVs from a prior `stop --delete-namespace` get cleaned on the next `stop --delete-volumes`
- Every k8s resource SO creates now carries `app.kubernetes.io/stack` via a new `ClusterInfo._stack_labels()` helper
- Closes so-l2l, so-076.2. Also includes pebble audit: closes so-c71, so-b2b, so-k1k; files so-328
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