k8s(cluster): pin m12-vsc-20260830, now running on all three voters

Built clean from 8aa1fbb. Staged roll partition 2 -> 1 -> 0 with a quorum-write
probe between each (201 every time); sts 3/3 updated=3, and all three voters report
build_hash=8aa1fbb4140ac720b360465073388fe5ad0f84a7 with no -dirty suffix.

Post-deploy, measured live: a non-unit query (|q|^2 = 132.4) now returns distances
of 1.7944-1.8059, inside the documented [0,4] and identical on all three replicas;
the same class of query returned 591-1174 before. A zero-norm query returns 400.
Per-group vector counts are now visible for all three shard groups (groups 1 and 2
had no series at all before) and read spread 0.

k8s/cluster/statefulset.yaml

@@ -100,7 +100,7 @@ spec:
               mountPath: /data
       containers:
         - name: tidaldb
-          image: registry.threesix.ai/tidal/server:m12-vector-grow-20260830@sha256:2f2357eae5af863804a85dba5514833c76730eeaac211e8da2cb60e797b34f92
+          image: registry.threesix.ai/tidal/server:m12-vsc-20260830@sha256:5c18d2b10f71d7ed63f776e45a7d4dba2889a52087b2eb11a6509afe0df0f1cf
           imagePullPolicy: IfNotPresent
           # The image ENTRYPOINT is the bare binary. We override the command with
           # a tiny /bin/sh wrapper (the bookworm-slim runtime HAS a shell) so we