fix(stacks): surface pull failures and log before/after image IDs on mismatch

update run silently swallowed pull errors and never logged what actually
differed, making a recurring false "updates found" for pulsenode (no
registry-side change since Aug 19) impossible to diagnose.

bin/stacks

@@ -417,11 +417,15 @@ _update_run() {
 
     local before after
     before=$(_stack_image_ids "$stack_dir" "${env_flag[@]+"${env_flag[@]}"}") || true
-    (cd "$stack_dir" && docker compose "${env_flag[@]}" pull 2>&1) || true
+    if ! (cd "$stack_dir" && docker compose "${env_flag[@]}" pull 2>&1); then
+      warn "  Pull reported a non-zero exit for $stack (see output above) — comparison may be unreliable"
+    fi
     after=$(_stack_image_ids "$stack_dir" "${env_flag[@]+"${env_flag[@]}"}") || true
 
     if [[ "$before" != "$after" ]]; then
       info "  Updates found — recreating $stack"
+      info "    before: ${before:-<empty>}"
+      info "    after:  ${after:-<empty>}"
       if (cd "$stack_dir" && docker compose "${env_flag[@]}" up -d 2>&1); then
         updated+=("$stack")
         ok "  $stack updated"