Count sent messages at send time; implement first-contact greeting

- messages_sent now increments when a message is queued (async_send_message),
  not only when a delivery proof returns. LXMessage's delivery callback only
  fires on a returned proof (LXMessage.py ~566), which many peers/methods never
  send, so the "Messages sent" sensor was stuck at 0 for messages that were
  actually delivered. The delivery callback now only emits the event.
- Implement the previously-inert "greeting" option: send it automatically the
  first time each sender contacts HA (tracked per sender in RuntimeData).
- Clarify the notify entity (rename to "Send message" / "Отправить сообщение")
  and document greeting + notify in strings/translations/README.

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

custom_components/reticulum/__init__.py

@@ -80,6 +80,8 @@ class RuntimeData:
         # Maps a peer address -> the HA conversation_id we opened for it, so
         # each remote user keeps its own Assist conversation context.
         self.conversation_ids: dict[str, str] = {}
+        # Senders we've already greeted this session (first-contact greeting).
+        self.greeted: set[str] = set()
 
 
 async def async_setup_entry(hass: HomeAssistant, entry: ConfigEntry) -> bool:
@@ -236,6 +238,12 @@ def _make_incoming_handler(
             _LOGGER.debug("Ignoring message from non-allowed sender %s", source)
             return
 
+        # First-contact greeting: send the configured greeting once per sender.
+        greeting = (options.get(CONF_GREETING) or "").strip()
+        if greeting and source not in runtime.greeted:
+            runtime.greeted.add(source)
+            await _reply(runtime.manager, source, greeting, "Home Assistant")
+
         if not options.get(CONF_ENABLE_ASSIST, True):
             return