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.

src/xmpp/jid.c

@@ -280,9 +280,13 @@ jid_fulljid_or_barejid(Jid* jid)
 gchar*
 jid_random_resource(void)
 {
-    auto_gchar gchar* rand = get_random_string(4);
+    gchar* rand = g_malloc0(29);
+    const gchar* digits = "0123456789";
 
-    gchar* result = g_strdup_printf("profanity.%s", rand);
+    for (int i = 0; i < 28; i++) {
+        rand[i] = digits[g_random_int_range(0, 10)];
+    }
+    rand[28] = '\0';
 
-    return result;
+    return rand;
 }