fix(ha-bootstrap): wire OP_requestVote RPC through standard Request envelope

The vote_request_thread was sending raw capnp(RequestVoteRequest) bytes
but the server-side iomgr decodes every incoming packet as a Request
struct. This caused the term field (uint64) to be misread as the opcode
field (uint16), so vote RPCs were silently misrouted (term=1 → OPCode_reply,
term=2 → OPCode_hello) and no node ever got a vote from its peers.

Fix:
- controller.capnp: add requestvotemsg @27 to Request.body and
  requestvotereplymsg @14 to RequestReply.data
- typemap.h: move request_vote_req_t/reply_t before xce_request_t;
  add requestvotemsg/requestvotereplymsg to body/data unions
- ha.c: rewrite vote_request_thread send/recv to use xce_encode()
  wrapper and decode outer Request→inner RequestReply on receive
- cluster.c: add case OPCode_requestVote handler calling
  handle_request_vote() and replying via xce_reply()

All 188 unit tests pass.

src/include/typemap.h

@@ -172,6 +172,20 @@ typedef struct {
     } data;
 } xce_update_data_t;
 
+typedef struct {
+    uint64_t  term;
+    char     *candidate_id;
+    uint64_t  config_tag;
+    uint64_t  last_log_lsn;
+} request_vote_req_t;
+
+typedef struct {
+    uint64_t term;
+    int      vote_granted;
+    uint64_t peer_config_tag;
+    uint64_t peer_last_log_lsn;
+} request_vote_reply_t;
+
 typedef struct {
     uint64_t seq;
     uint32_t opcode;
@@ -186,6 +200,7 @@ typedef struct {
         repl_config_push_reply_t*  replconfigpushreplymsg;
         upgrade_config_reply_t*    upgradeconfigreplymsg;
         ctrl_hello_reply_t*        ctrlhelloreplymsg;
+        request_vote_reply_t*      requestvotereplymsg;
     } data;
     /* Req 7: standby redirect fields — populated when status == XCE_ERR_STANDBY */
     char    *redirect_host;
@@ -221,6 +236,7 @@ typedef struct {
         upgrade_config_req_t*     upgradeconfigrequestmsg;
         heartbeat_msg_t*          heartbeatmsg;
         ctrl_hello_req_t*         ctrlhellomsg;
+        request_vote_req_t*       requestvotemsg;
         void*                     walcatchupentrymsg;    /* wal_catchup_entry_t* */
         void*                     snapshottransfermsg;   /* snapshot_transfer_t* */
     } body;
@@ -229,21 +245,9 @@ typedef struct {
 /* ── HA election and replication Cap'n Proto mapped types ────────────────
  * C-side counterparts for the HA protocol capnp structs added in the
  * ha-config-bootstrap spec (controller.capnp structs with $C.mapname).
- * Must be declared here so controller.capnp.h can reference them.       */
-
-typedef struct {
-    uint64_t  term;
-    char     *candidate_id;
-    uint64_t  config_tag;
-    uint64_t  last_log_lsn;
-} request_vote_req_t;
-
-typedef struct {
-    uint64_t term;
-    int      vote_granted;
-    uint64_t peer_config_tag;
-    uint64_t peer_last_log_lsn;
-} request_vote_reply_t;
+ * Must be declared here so controller.capnp.h can reference them.
+ * request_vote_req_t and request_vote_reply_t are defined above
+ * xce_reply_t so they can be used in the xce_request_t body union. */
 
 typedef struct {
     char *name;