expose whether a volume replica is backed by remote storage

Volume locations returned by lookups do not indicate whether a replica
has been tiered to remote storage. Readers cannot distinguish a local
replica from a remote-backed one, so they may hit a remote-backed
replica first even when a local replica is available.

Add DataInRemote to the lookup location message, populate it from the
master's volume info, and carry it through the wdclient vid map so
clients can prefer local replicas when resolving chunk locations.

other/java/client/src/main/proto/filer.proto

@@ -576,6 +576,7 @@ message Location {
     string public_url = 2;
     uint32 grpc_port = 3;
     string data_center = 4;
+    bool data_in_remote = 5;
 }
 message LookupVolumeResponse {
     map<string, Locations> locations_map = 1;
@@ -662,6 +663,7 @@ message SubscribeMetadataResponse {
     int64 ts_ns = 3;
     repeated SubscribeMetadataResponse events = 4; // batch of additional events (backlog catch-up)
     repeated LogFileChunkRef log_file_refs = 5;    // log file chunk refs for client direct-read
+    int64 flushed_ts_ns = 6; // local log-buffer flush watermark: everything at or below it is on disk
 }
 message ListMetadataSubscribersRequest {
     repeated string client_types = 1; // optional filter by client type, e.g. "mount"; empty = all