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/README.md

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+# Technitium DNS - Home Assistant Add-on
+
+Runs the [Technitium DNS Server](https://technitium.com/dns/) inside Home Assistant as a supervised add-on.
+
+## Features
+- Ad-blocking DNS server with web console on port 5380
+- Local DNS records, conditional forwarding, DNS-over-TLS/HTTPS
+- Persists config to the add-on config volume
+- Designed to act as **secondary** to a primary Technitium instance via DNS Replication
+
+## Installation
+
+1. Add this repository in Home Assistant:
+   **Settings → Add-ons → Add-on Store → ⋮ → Repositories**
+   ```
+   https://git.kenschiano.net/kschiano/Hassio_Addons.git
+   ```
+2. Refresh the add-on store, then install **Technitium DNS**.
+3. Set `admin_password` and `timezone` in the add-on config.
+4. Start the add-on and open the web UI at `http://homeassistant.local:5380`.
+
+## Failover / Replication setup
+
+This add-on is intended to run as a **secondary** to a primary Technitium instance deployed to Kubernetes. See the repository root README for the full primary/secondary replication plan.
+
+Quick steps:
+1. On the **Primary** (k8s): Settings → Replication → generate API key, add this host as secondary (`https://homeassistant.local:5380`).
+2. On this add-on: Settings → Replication → set the same API key, enable secondary mode.
+
+## Updating the add-on
+
+The add-on pulls `technitium/dns-server:latest` upstream. To update:
+1. Rebuild the add-on image: **Settings → Add-ons → Technitium DNS → Rebuild**
+2. Or restart the add-on after bumping `version` in `config.yaml`.
+
+## Repository
+
+Source: https://git.kenschiano.net/kschiano/Hassio_Addons