refactor(docker): docker-compose.yml ist der Pull-Weg, Bauen wandert nach .dev.yml

Namen getauscht: das Standard-Compose zieht jetzt die fertigen Registry-Images
(vorher docker-compose.prod.yml), die Build-Variante heisst docker-compose.dev.yml.
Weniger verwirrend, weil der Produktivfall ohne -f auskommt. Kopfkommentare,
README, CLAUDE.md, .env.example und build-push-images.mjs entsprechend angepasst.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

.env.example

@@ -1,6 +1,6 @@
 # Copy to .env next to your docker-compose file and fill in.  cp .env.example .env
-# Used by docker-compose.yml (builds locally from the Dockerfiles).
-# The REGISTRY/TAG at the bottom are only for the optional pull-from-registry / CI flow.
+# Used by docker-compose.yml (zieht fertige Images) und docker-compose.dev.yml (baut lokal).
+# REGISTRY/TAG unten braucht nur der Pull-Weg (docker-compose.yml).
 
 # ── URLs pre-filled on the frontend setup screen ─────────────────────────────
 NAVIDROME_URL=https://music.example.com
@@ -23,7 +23,7 @@ GITEA_REPO=Docker/NovaSonic
 GITEA_TOKEN=                              # read token (only needed for a private repo)
 GITEA_APK_TAG=apk-latest
 
-# ── Pre-built images (docker-compose.yml only) ───────────────────────────────
+# ── Fertige Images (nur docker-compose.yml) ──────────────────────────────────
 # REGISTRY = where `npm run push-images` pushed to and where the host pulls from.
 #   Gitea container registry (lowercase owner):  gitea.honeyy.duckdns.org/docker
 #   Docker Hub:                                  docker.io/youruser