fix(docker): drop image: field so compose never pulls service image

Image: ttrpg-app:local named a registry image. Without --build flag,
compose tried pull first -> 'pull access denied' (private, unpublished).
Then fell back to build. Confusing error.

Removed image: field. Compose now auto-names (docker-app), always builds
local, never attempts registry pull. Base images (node/caddy) pull once
on first build, then cache. No pull_policy needed.

docker compose up (from docker/ dir) now works clean.

docker/docker-compose.yml

@@ -3,12 +3,13 @@
 #   docker compose -f docker/docker-compose.yml up --build
 services:
   app:
+    # no image: field => compose auto-names (docker-app), never pulls,
+    # always builds local. Service image private, never published.
     build:
       context: ..
       dockerfile: docker/Dockerfile
       args:
         - REACT_APP_TRACKER_APP_ID=${TRACKER_APP_ID:-ttrpg-initiative-tracker-default}
-    image: ttrpg-app:local
     ports:
       - "${PORT:-8080}:80"
     volumes: