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/proftest.c

@@ -601,11 +601,11 @@ prof_connect_with_roster(const char* roster)
     assert_true(prof_output_regex(".+online.+ \\(priority 0\\)\\."));
 
     expect_timeout = EXPECT_TIMEOUT_CONNECT;
-    // Wait for presence stanza to be sent (content-based, not ID-based)
+    // Wait for presence stanza to be sent
     // Match the actual attribute order from stanza_attach_caps
     assert_true(stbbr_received(
         "<presence id=\"*\">"
-        "<c xmlns=\"http://jabber.org/protocol/caps\" hash=\"sha-1\" node=\"http://profanity-im.github.io\" ver=\"*\"/>"
+        "<c xmlns=\"http://jabber.org/protocol/caps\" hash=\"sha-1\" node=\"*\" ver=\"*\"/>"
         "</presence>"));
 }