fix(xmpp): obfuscate client identity in protocol exchanges

Modify version responses to return a generic client name and omit
version strings. Drop the "profanity." prefix from dynamically
generated JID resources. Spoof the XEP-0115 capabilities node URI to
prevent service discovery/presence fingerprinting. These adjustments
reduce the client's attack surface by minimizing identifiable metadata.

tests/functionaltests/test_export_import.c

@@ -1289,7 +1289,7 @@ _join_muc(const char* room)
     snprintf(presence, sizeof(presence),
         "<presence id='*' lang='en' to='stabber@localhost/profanity' from='%s/stabber'>"
             "<c hash='sha-1' xmlns='http://jabber.org/protocol/caps' "
-               "node='http://profanity-im.github.io' ver='*'/>"
+               "node='*' ver='*'/>"
             "<x xmlns='http://jabber.org/protocol/muc#user'>"
                 "<item role='participant' jid='stabber@localhost/profanity' affiliation='none'/>"
             "</x>"