fix(settings): hold the channel test until changes are saved

The webhook, ntfy, email and Telegram test routes send through the
saved channel config. After a field changed, the card kept showing the
Saved note from the last save and Test still ran, so it reported on the
old settings: a webhook switched to the Gotify format was tested with
the generic body and Gotify refused it. The note now disappears on a
change, and the test button stays off with a save-first hint while the
form differs from what is saved. Refs #947

messages/de.json

@@ -6133,6 +6133,7 @@
     },
     "testConnection": {
       "test": "Verbindung testen",
+      "saveFirst": "Speichere zuerst deine Änderungen. Der Test nutzt die gespeicherten Einstellungen.",
       "testing": "Teste…",
       "ok": "Verbunden (Latenz {latency} ms)",
       "errors": {