Match Go VolumeCopy: reject when no suitable disk location exists

Go returns ErrVolumeNoSpaceLeft when no location matches the disk type
and has sufficient space. Rust had an unsafe fallback that silently
picked the first location regardless of type or available space.

seaweed-volume/src/server/grpc_server.rs

@@ -944,11 +944,6 @@ impl VolumeServer for VolumeGrpcService {
                     }
                 }
             }
-            // Fallback: use first location if no disk type match
-            if found.is_none() && !store.locations.is_empty() {
-                let loc = &store.locations[0];
-                found = Some((loc.directory.clone(), loc.idx_directory.clone()));
-            }
             found.ok_or_else(|| Status::internal(format!("no space left {}", disk_type)))?
         };