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

pyproject.toml

@@ -1,6 +1,6 @@
 [project]
 name = "directdnsonly"
-version = "1.0.9"
+version = "2.1.0"
 description = "DNS Management System - DirectAdmin to multiple backends"
 authors = [
     {name = "Aaron Guise",email = "aaron@guise.net.nz"}