Skip locally built images by their build: stanza instead of a list of names

update-containers kept LOCAL_BUILD, a hand-written list of services whose
images are built on the machine, so it would not try to pull them. The
compose files already say this. A service with a build: stanza names a
local image, and there is nothing in a registry to pull.

images_for now drops the image of any compose service that has a build:
stanza. Those services resolve no images, and the run skips them without a
log line. The list, and the app names it carried, are gone. On the VPS,
--list resolves the same images as before for every other service.

server/scripts/update-containers

@@ -46,10 +46,6 @@ set -uo pipefail
 #   podman pull <image> && systemctl --user restart podman-<name>.service
 SKIP=(postgresql authentik watchtower)
 
-# Services built locally rather than pulled. There is no registry image to check,
-# so pulling is pointless — they are skipped automatically when no `image:` line
-# resolves, but listing them here keeps the log quiet and the intent obvious.
-LOCAL_BUILD=(bang completeuphoria sierraandtyler)
 
 # ⚠️ NOTE ON GITEA: it is deliberately NOT in SKIP. The three-day outage was caused
 # by watchtower's recreate mechanism, not by the act of updating — restarting the
@@ -90,8 +86,10 @@ list_units() {
         | sort
 }
 
-# Images declared in a service's compose.yml. Ignores commented lines and the
-# `build:` stanza, which has no pullable image.
+# Images declared in a service's compose.yml. Ignores commented lines, and the
+# image of any compose service that has a `build:` stanza: that tag names a
+# locally built image, so there is nothing in a registry to pull. Those
+# services therefore resolve no images and are skipped without a log line.
 #
 # Image tags frequently reference variables from the service's .env, e.g.
 #   ghcr.io/get-convex/convex-backend:${BACKEND_TAG:-latest}
@@ -102,8 +100,22 @@ list_units() {
 images_for() {
     local dir="$1"
     [ -f "$dir/compose.yml" ] || return 0
-    grep -oE '^[[:space:]]*image:[[:space:]]*[^[:space:]#]+' "$dir/compose.yml" 2>/dev/null \
-        | sed -E 's/^[[:space:]]*image:[[:space:]]*//' \
+    awk '
+        function flush() { if (img != "" && !build) print img; img = ""; build = 0 }
+        /^[[:space:]]*#/ { next }
+        /^services:[[:space:]]*$/ { in_services = 1; indent = -1; next }
+        in_services && /^[^[:space:]]/ { flush(); in_services = 0 }
+        in_services && NF {
+            match($0, /^ */); here = RLENGTH
+            if (indent < 0) indent = here
+            if (here == indent && $0 ~ /^ *[A-Za-z0-9_.-]+:[[:space:]]*$/) { flush(); next }
+            if ($0 ~ /^[[:space:]]+build:/) build = 1
+            if (match($0, /^[[:space:]]+image:[[:space:]]*[^[:space:]#]+/)) {
+                img = substr($0, RSTART, RLENGTH); sub(/^[[:space:]]+image:[[:space:]]*/, "", img)
+            }
+        }
+        END { flush() }
+    ' "$dir/compose.yml" 2>/dev/null \
         | while IFS= read -r img; do
               case "$img" in
                   *'${'*) ( set -a; [ -f "$dir/.env" ] && . "$dir/.env" >/dev/null 2>&1; set +a
@@ -124,8 +136,8 @@ if [ "${LIST:-0}" = "1" ]; then
     for svc in $(list_units); do
         printf '%-22s' "$svc"
         if in_list "$svc" "${SKIP[@]}";        then echo "SKIP (frozen)"; continue; fi
-        if in_list "$svc" "${LOCAL_BUILD[@]}"; then echo "SKIP (built locally)"; continue; fi
-        echo "$(images_for "$(workdir_for "$svc")" | tr '\n' ' ')"
+        imgs="$(images_for "$(workdir_for "$svc")" | tr '\n' ' ')"
+        echo "${imgs:-(built locally, nothing to pull)}"
     done
     exit 0
 fi
@@ -142,7 +154,6 @@ for svc in $(list_units); do
     [ -n "$ONLY" ] && [ "$svc" != "$ONLY" ] && continue
     if [ -z "$ONLY" ]; then
         in_list "$svc" "${SKIP[@]}"        && { log "  $svc: frozen (SKIP list)"; continue; }
-        in_list "$svc" "${LOCAL_BUILD[@]}" && continue
     fi
 
     # ⚠️ NEVER resurrect a service that is deliberately stopped. `systemctl restart`