fix: medium priority warnings - write-strings and unused variables

1. Fix write-strings warnings (12 occurrences):
   - MySQL_HostGroups_Manager.cpp: Change char* to const char*
     for src_status and dst_status variables
   - MySQL_Monitor.cpp: Change ConsumerThread constructor
     parameter from char thread_name[16] to const char *thread_name

2. Fix unused-but-set-variable warnings (6 occurrences) by
   wrapping PROXYSQLGENAI-specific variables in #ifdef blocks:
   - stats_mcp_query_tools_counters
   - stats_mcp_query_tools_counters_reset
   - stats_mcp_query_digest
   - stats_mcp_query_digest_reset
   - stats_mcp_query_rules
   - runtime_mcp_query_rules

   These variables were assigned values but appeared unused when
   PROXYSQLGENAI was not defined. Now they are only defined and
   assigned when PROXYSQLGENAI is enabled.

This eliminates 18 compiler warnings: 12 write-strings and 6
unused-but-set-variable warnings.

Found during compiler warning analysis with 'make debug'.

lib/MySQL_HostGroups_Manager.cpp

@@ -3783,8 +3783,8 @@ void MySQL_HostGroups_Manager::set_Readyset_status(char *hostname, int port, enu
 				if (mysrvc->port==port && strcmp(mysrvc->address,hostname)==0) {
 					enum MySerStatus prev_status = mysrvc->get_status();
 					if (prev_status != status) {
-						char *src_status = "?"; // this shouldn't display
-						char *dst_status = "?"; // this shouldn't display
+						const char *src_status = "?"; // this shouldn't display
+						const char *dst_status = "?"; // this shouldn't display
 						if (prev_status == MYSQL_SERVER_STATUS_ONLINE) { src_status = "ONLINE"; }
 						else if (prev_status == MYSQL_SERVER_STATUS_OFFLINE_SOFT) { src_status = "OFFLINE_SOFT"; }
 						else if (prev_status == MYSQL_SERVER_STATUS_SHUNNED) { src_status = "SHUNNED"; };

lib/MySQL_Monitor.cpp

@@ -105,7 +105,7 @@ class ConsumerThread : public Thread {
 	int thrn;
 	char thr_name[16];
 	public:
-	ConsumerThread(wqueue<WorkItem<T>*>& queue, int _n, char thread_name[16]=NULL) : m_queue(queue) {
+	ConsumerThread(wqueue<WorkItem<T>*>& queue, int _n, const char *thread_name=NULL) : m_queue(queue) {
 		thrn=_n;
 		if (thread_name && thread_name[0]) {
 			snprintf(thr_name, sizeof(thr_name), "%.16s", thread_name);

lib/ProxySQL_Admin.cpp

@@ -1202,11 +1202,13 @@ bool ProxySQL_Admin::GenericRefreshStatistics(const char *query_no_space, unsign
 	bool stats_memory_metrics=false;
 	bool stats_mysql_commands_counters=false;
 	bool stats_pgsql_commands_counters = false;
+#ifdef PROXYSQLGENAI
 	bool stats_mcp_query_tools_counters = false;
 	bool stats_mcp_query_tools_counters_reset = false;
 	bool stats_mcp_query_digest = false;
 	bool stats_mcp_query_digest_reset = false;
 	bool stats_mcp_query_rules = false;
+#endif
 	bool stats_mysql_query_rules=false;
 	bool stats_pgsql_query_rules = false;
 	bool stats_mysql_users=false;
@@ -1234,7 +1236,9 @@ bool ProxySQL_Admin::GenericRefreshStatistics(const char *query_no_space, unsign
 	bool runtime_pgsql_query_rules = false;
 	bool runtime_pgsql_query_rules_fast_routing = false;
 
+#ifdef PROXYSQLGENAI
 	bool runtime_mcp_query_rules = false;
+#endif
 
 	bool stats_pgsql_global = false;
 	bool stats_pgsql_connection_pool = false;
@@ -1398,6 +1402,7 @@ bool ProxySQL_Admin::GenericRefreshStatistics(const char *query_no_space, unsign
 		{ stats_proxysql_message_metrics=true; refresh=true; }
 	if (strstr(query_no_space,"stats_proxysql_message_metrics_reset"))
 		{ stats_proxysql_message_metrics_reset=true; refresh=true; }
+#ifdef PROXYSQLGENAI
 	if (strstr(query_no_space,"stats_mcp_query_tools_counters"))
 		{ stats_mcp_query_tools_counters=true; refresh=true; }
 	if (strstr(query_no_space,"stats_mcp_query_tools_counters_reset"))
@@ -1408,6 +1413,7 @@ bool ProxySQL_Admin::GenericRefreshStatistics(const char *query_no_space, unsign
 		{ stats_mcp_query_digest=true; refresh=true; }
 	if (strstr(query_no_space,"stats_mcp_query_rules"))
 		{ stats_mcp_query_rules=true; refresh=true; }
+#endif
 
 	// temporary disabled because not implemented
 /*
@@ -1494,9 +1500,11 @@ bool ProxySQL_Admin::GenericRefreshStatistics(const char *query_no_space, unsign
 			if (strstr(query_no_space, "runtime_pgsql_query_rules_fast_routing")) {
 				runtime_pgsql_query_rules_fast_routing = true; refresh = true;
 			}
+#ifdef PROXYSQLGENAI
 			if (strstr(query_no_space, "runtime_mcp_query_rules")) {
 				runtime_mcp_query_rules = true; refresh = true;
 			}
+#endif
 			if (strstr(query_no_space,"runtime_scheduler")) {
 				runtime_scheduler=true; refresh=true;
 			}