Reinstate greeting as an auto-reply used only when Assist is off

The greeting option returns, but it is now sent as an automatic reply to
incoming messages only when "Route incoming messages to Assist" is disabled,
so senders get an acknowledgement instead of silence. When Assist handles
messages the greeting is not used. Blank disables it.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

custom_components/reticulum/manifest.json

@@ -12,5 +12,5 @@
   "loggers": ["RNS", "LXMF"],
   "requirements": ["rns>=0.9.0", "lxmf>=0.6.0"],
   "single_config_entry": true,
-  "version": "1.0.7"
+  "version": "1.0.8"
 }