feat: add Technitium DNS Home Assistant add-on

- repository.yaml manifest for HA add-on store
- technitium_dns add-on using upstream technitium/dns-server image
- config.yaml with ports 53/udp, 53/tcp, 5380/tcp and password schema
- Dockerfile symlinks /etc/dns to /data/dns for persistent config
- READMEs for repo and add-on

technitium_dns/Dockerfile

@@ -0,0 +1,14 @@
+ARG BUILD_FROM=ghcr.io/hassio-addons/base:latest
+FROM technitium/dns-server:latest
+
+# Home Assistant add-on requirements
+ENV DATA_DIR="/data/dns"
+
+# Technitium stores its config in /etc/dns by default; use the add-on data
+# directory so settings persist across restarts.
+RUN mkdir -p /data/dns && \
+    ln -s /data/dns /etc/dns
+
+# Home Assistant expects a run command via S6/entrypoint; Technitium ships its own.
+ENTRYPOINT []
+CMD ["dotnet", "DnsServerApp.dll"]