Remove the greeting feature entirely

Drops the CONF_GREETING option, the first-contact greeting logic and its
RuntimeData state, and all related strings/translations/README text. Any
greeting value left in an existing entry's options is simply ignored.

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

custom_components/reticulum/translations/en.json

@@ -37,7 +37,6 @@
           "allow_all_senders": "Reply to any sender",
           "allowed_identities": "Allowed sender addresses",
           "default_recipient": "Default recipient address (for the notify entity)",
-          "greeting": "First-contact greeting message",
           "delivery_method": "Default delivery method",
           "announce_interval": "Announce interval",
           "propagation_node": "Propagation node address",
@@ -48,7 +47,6 @@
           "enable_assist": "When enabled, incoming LXMF messages are answered by the Assist conversation agent and the reply is sent back over Reticulum.",
           "allowed_identities": "One address per line (or comma separated). Only used when 'Reply to any sender' is off.",
           "default_recipient": "16-byte hex LXMF address that the notify.reticulum entity sends to.",
-          "greeting": "Sent automatically the first time each sender messages Home Assistant (once per sender per restart). Leave blank to disable.",
           "announce_interval": "How often (seconds) to announce our address. 0 disables periodic announces.",
           "propagation_node": "Optional LXMF propagation node for store-and-forward delivery.",
           "sync_interval": "How often (seconds) to pull queued messages from the propagation node. 0 disables."