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/schema/controller.capnp

@@ -558,6 +558,7 @@ struct RequestReply $C.mapname("xce_reply_t"){
     replconfigpushreplymsg   @9: ReplConfigPushReply;
     upgradeconfigreplymsg    @10: UpgradeConfigReply;
     ctrlhelloreplymsg        @13: CtrlHelloReply;
+    requestvotereplymsg      @14: RequestVoteReply;
   }
 
   redirectHost @11: Text   $C.mapname("redirect_host");
@@ -623,6 +624,7 @@ struct Request $C.mapname("xce_request_t"){
     upgradeconfigrequestmsg    @24: UpgradeConfigRequest;
     heartbeatmsg               @25: HeartbeatMsg;
     ctrlhellomsg               @26: CtrlHelloRequest;
+    requestvotemsg             @27: RequestVoteRequest;
   }
 }