feat: replace debug view polling with real-time SignalR streaming

The debug view polled every 2s by re-subscribing for full snapshots. Now a
persistent DebugStreamBridgeActor on central subscribes once and receives
incremental Akka stream events from the site, forwarding them to the Blazor
component via callbacks and to the CLI via a new SignalR hub at
/hubs/debug-stream. Adds `debug stream` CLI command with auto-reconnect.

src/ScadaLink.CLI/README.md

@@ -1038,6 +1038,25 @@ scadalink --url <url> debug snapshot --id <int>
 
 The command resolves the instance's site internally and routes the request to the correct site cluster. Returns all attribute values (name, value, quality, timestamp) and alarm states (name, state, priority, timestamp) at the moment the request reaches the site.
 
+#### `debug stream`
+
+Stream live attribute values and alarm state changes in real-time using a SignalR WebSocket connection to the central server's `/hubs/debug-stream` hub. Events are printed as they arrive. Press Ctrl+C to disconnect.
+
+```sh
+scadalink --url <url> debug stream --id <int>
+```
+
+| Option | Required | Description |
+|--------|----------|-------------|
+| `--id` | yes | Instance ID |
+
+The default JSON format outputs one NDJSON object per event line with a `type` field (`snapshot`, `attributeChanged`, or `alarmChanged`). Table format (`--format table`) shows a formatted initial snapshot followed by streaming rows prefixed with `ATTR` or `ALARM`.
+
+Features:
+- Automatic reconnection on connection loss with re-subscribe.
+- Works through the Traefik load balancer (WebSocket upgrade proxied natively).
+- Requires the `Deployment` role.
+
 ---
 
 ### `audit-log` — Audit log queries