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>

checkmk/compose.yaml

@@ -1,6 +1,6 @@
 services:
   checkmk:
-    image: "checkmk/check-mk-raw:2.4.0-latest"
+    image: "checkmk/check-mk-raw:2.4.0-2026.09.14"
     container_name: "checkmk"
     restart: unless-stopped
     # ports:

checkmk/k8s/checkmk.yaml

@@ -31,7 +31,7 @@ spec:
     spec:
       containers:
         - name: checkmk
-          image: checkmk/check-mk-raw:2.4.0-latest
+          image: checkmk/check-mk-raw:2.4.0-2026.09.14
           envFrom:
             - secretRef:
                 name: checkmk-secrets