chore(images): pin service image updates

Replace floating service images with reviewable tags or digests.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

termix/compose.yaml

@@ -1,6 +1,6 @@
 services:
   termix:
-    image: ghcr.io/lukegus/termix:latest
+    image: ghcr.io/lukegus/termix:2.7.1
     container_name: termix
     restart: unless-stopped
     # ports:

termix/k8s/termix.yaml

@@ -27,7 +27,7 @@ spec:
     spec:
       containers:
         - name: termix
-          image: ghcr.io/lukegus/termix:latest
+          image: ghcr.io/lukegus/termix:2.7.1
           envFrom:
             - configMapRef:
                 name: termix-config