fix: enable docker-socket-proxy container restart (ALLOW_RESTARTS)

The service's own comment already claimed "list/inspect/exec/restart
existing containers" capability, but ALLOW_RESTARTS was never actually set
-- restart was silently unavailable. Needed for argus-appliance#43's new
Diagnostics "Restart Container" recovery action, which is the first real
caller.

Deliberately narrow, per explicit product decision: restart only (stop/
restart/kill on an *existing* container). create/prune remain denied by
the haproxy template's own explicit deny-list regardless of this or any
POST setting. start/stop (ALLOW_START/ALLOW_STOP) deliberately left unset
-- nothing needs them yet.

docker-compose.yml

@@ -73,6 +73,14 @@ services:
       EXEC: 1
       VERSION: 1
       POST: 1
+      # Restart (stop/restart/kill on an *existing* container) only --
+      # create/prune stay denied by the haproxy template's own explicit
+      # deny-list regardless of POST, and start/stop stay off (ALLOW_START/
+      # ALLOW_STOP unset) since nothing needs them yet. This comment block's
+      # own claim of "restart" capability (above) was aspirational until
+      # this line existed -- appliance#43's Diagnostics recovery actions are
+      # the first real caller.
+      ALLOW_RESTARTS: 1
     volumes:
       - /var/run/docker.sock:/var/run/docker.sock:ro
       - ./docker-socket-proxy/haproxy.cfg.template:/usr/local/etc/haproxy/haproxy.cfg.template:ro