feat: conditional BIND startup; config search path priority fix 🔧

- entrypoint: only start named when a bind backend is configured and
  enabled in app.yml; CoreDNS-only deployments skip named entirely
- config: user-supplied paths (/etc/directdnsonly, ./config) now
  searched before the bundled app.yml so mounted configs take effect
- docs: deployment topology reference — Topology A (dual BIND HA) and
  Topology B (single instance, multi-DC CoreDNS MySQL)
- chore: bump version to 2.1.0
- justfile: add build-docker recipe

justfile

@@ -87,6 +87,9 @@ build:
         directdnsonly/main.py
     rm -f *.spec
 
+build-docker:
+    export DOCKER_CONFIG="/home/guisea/.docker/guisea" && \
+    docker buildx build --platform linux/amd64,linux/arm64 -t guisea/directdnsonly:dev --push --progress plain --file Dockerfile .
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 # Clean
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