Gluetun/Valkey: use fully-qualified docker.io image names

The host has no unqualified-search registries in registries.conf, so the
short names qmcgaw/gluetun and valkey/valkey did not resolve and the pull
hung. Qualify them with docker.io/ so the pull works on any host.

dankclaw/compose.yaml

@@ -5,7 +5,7 @@
 services:
   # --- VPN tunnel: SearXNG outbound traffic only ---------------------------
   gluetun:
-    image: qmcgaw/gluetun:latest
+    image: docker.io/qmcgaw/gluetun:latest
     container_name: gluetun
     restart: always
     cap_add:
@@ -51,7 +51,7 @@ services:
       retries: 3
 
   valkey:
-    image: valkey/valkey:9-alpine
+    image: docker.io/valkey/valkey:9-alpine
     container_name: searxng-valkey
     restart: always
     volumes: