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/stanza.c

@@ -935,16 +935,17 @@ stanza_create_caps_query_element(xmpp_ctx_t* ctx)
     xmpp_stanza_set_attribute(identity, "category", "client");
 
     ProfAccount* account = accounts_get_account(session_get_account_name());
+    gchar* client = account->client;
+    account_free(account);
 
-    auto_gchar gchar* name = g_strdup(account->client ? account->client : "Pidgin");
+    auto_gchar gchar* name = g_strdup(client ? client : "Pidgin");
 
-    if (account->client) {
+    if (client) {
         gchar* space = strchr(name, ' ');
         if (space) {
             *space = '\0';
         }
     }
-    account_free(account);
 
     xmpp_stanza_set_attribute(identity, "name", name);
     xmpp_stanza_add_child(query, identity);