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. Clear the XEP-0115 capabilities node URI to
prevent service discovery fingerprinting. These adjustments reduce the
client's attack surface by minimizing identifiable metadata.

tests/functionaltests/test_connect.c

@@ -25,7 +25,7 @@ connect_jid_sends_presence_after_receiving_roster(void **state)
 
     assert_true(stbbr_received(
         "<presence id='*'>"
-            "<c hash='sha-1' xmlns='http://jabber.org/protocol/caps' ver='*' node='http://profanity-im.github.io'/>"
+            "<c hash='sha-1' xmlns='http://jabber.org/protocol/caps' ver='*' node='*'/>"
         "</presence>"
     ));
 }