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>

searxng/compose.yaml

@@ -3,7 +3,7 @@
 services:
   core:
     container_name: searxng-core
-    image: docker.io/searxng/searxng:${SEARXNG_VERSION:-latest}
+    image: docker.io/searxng/searxng:${SEARXNG_VERSION:-2026.09.13-d4ce87c23}
     restart: unless-stopped
     # ports:
     # - ${SEARXNG_PORT:-8080}
@@ -31,7 +31,7 @@ services:
 
   valkey:
     container_name: searxng-valkey
-    image: docker.io/valkey/valkey:9-alpine
+    image: docker.io/valkey/valkey:9.1.2-alpine
     command: valkey-server --save 30 1 --loglevel warning
     restart: unless-stopped
     volumes: