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

docker/entrypoint.sh

@@ -1,12 +1,44 @@
 #!/bin/bash
+set -e
 
-# Start BIND
-/usr/sbin/named -u bind -f &
+# ---------------------------------------------------------------------------
+# Detect whether any bind backend is configured and enabled.
+# Uses the same config search order as the application itself.
+# ---------------------------------------------------------------------------
+BIND_ENABLED=$(python3 - <<'EOF'
+import yaml, sys, os
 
-## Initialize MySQL schema if needed
-#if [ -f /app/schema/coredns_mysql.sql ]; then
-#    mysql -h mysql -u root -prootpassword coredns < /app/schema/coredns_mysql.sql
-#fi
+config_paths = [
+    "/etc/directdnsonly/app.yml",
+    "/etc/directdnsonly/app.yaml",
+    "/app/app.yml",
+    "/app/app.yaml",
+    "/app/config/app.yml",
+    "/app/config/app.yaml",
+]
+
+config = {}
+for path in config_paths:
+    if os.path.exists(path):
+        with open(path) as f:
+            config = yaml.safe_load(f) or {}
+        break
+
+backends = config.get("dns", {}).get("backends", {})
+for cfg in backends.values():
+    if isinstance(cfg, dict) and cfg.get("type") == "bind" and cfg.get("enabled", False):
+        print("true")
+        sys.exit(0)
+print("false")
+EOF
+)
+
+if [ "$BIND_ENABLED" = "true" ]; then
+    echo "[entrypoint] BIND backend enabled — starting named"
+    /usr/sbin/named -u bind -f &
+else
+    echo "[entrypoint] No BIND backend configured — skipping named"
+fi
 
 # Start the application
-poetry run python directdnsonly/main.py
+exec python -m directdnsonly