Adds a new home-manager module `ntfy-notify` that delivers kanban state changes as Linux desktop notifications via **ntfy.sh** + `notify-send` → SwayNC.
**What it does:**
- Installs `ntfy` package
- Creates `~/.config/ntfy/client.yml` with subscription to the `joao-kanban` topic
- Sets up `ntfy-notify.service` (systemd --user) as a persistent subscriber
- Each incoming message fires `notify-send -u critical` → picked up by SwayNC
- Configurable: `server` URL, `subscriptions` list, per-topic priority
**Usage:**
After deploy, start the service once:
```bash
systemctl --user daemon-reload
systemctl --user start ntfy-notify
```
**Companion:** A cron job on the VPS will be needed to push kanban events to the ntfy topic (separate task).
Closes kanban task t_322419fa on ndots board.
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Co-authored-by: hermes-bot <hermes@srv1239749>
Reviewed-on: #1
