feat: wire ha_state_t into cluster_t + HA startup/shutdown lifecycle (P1-5)

src/include/xce/cluster_def.h

@@ -16,6 +16,9 @@
 #include "netio.h"
 #include "persist.h"
 #include "vtaskmgr.h"
+
+/* ha.h forward-declares cluster_t; including it here is safe (no circular dep) */
+#include "ha.h"
 #include "xce/types.h"
 #include "xlist.h"
 #include "zarray.h"
@@ -116,6 +119,7 @@ typedef struct cluster_s {
     cbuf_t              wbuf;
     int                 running;
     persist_t           persist;   /* Persistence module — P0-F */
+    ha_state_t          ha;        /* HA role management — P1-5 */
 } cluster_t;
 
 #endif /* XCE_CLUSTER_DEF_H */