pin filebrowser, couchdb, statping to explicit versions instead of floating beta/dev/untagged

Same category of risk as the gitea :nightly issue: floating dev/beta tags
let watchtower silently pull unvetted upstream builds. couchdb had no tag
at all (implicit :latest); filebrowser and statping only publish
beta/dev channels upstream so pinned to the exact version in use rather
than a moving target.

statping/docker-compose.yml

@@ -1,7 +1,11 @@
 services:
   statping:
     container_name: statping
-    image: statping/statping:dev
+    # statping upstream is abandoned (no pushes in 5+ years); pinned to the
+    # last tagged stable release instead of the floating :dev tag. Not
+    # currently deployed (no running container) — worth reconsidering
+    # whether this service is needed at all before ever starting it.
+    image: statping/statping:v0.90.74
     restart: always
     volumes:
       - /srv/statping-data:/app