s3vectors: name weed-vector processes servers (#12627)

* s3vectors: call the registered weed-vector processes servers

The gateway's discovery named them workers, the name of the admin
plugin workers. Also drops two comments left without a function.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_011UpvafvK8JpagF94MHWqwK

* test/s3vectors: build the Enterprise engine as weed-vector

In an Enterprise checkout, make ./weed-vector builds the distributed
engine, which also serves VectorService, instead of a separate
weed-vector-worker. An open-source checkout builds weed-vector-server
as before.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_011UpvafvK8JpagF94MHWqwK

* test/s3vectors: distributed mode starts two more weed-vector engines

It started weed-vector-worker, which no target builds now, and waited
for a gateway log line that no longer exists. The Enterprise
weed-vector's engines all join the placement controller.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_011UpvafvK8JpagF94MHWqwK

---------

Co-authored-by: Claude Opus 5.5 <noreply@anthropic.com>

weed/command/s3.go

@@ -734,9 +734,9 @@ func (s3opt *S3Options) startLanceServer(listenOnLocalhost bool) *http.Server {
 	return httpS
 }
 
-// vectorsRouter builds the S3 Vectors API router — workers register to the
-// master and the backend resolves them lazily, so a worker that comes up
-// after the gateway still gets picked up on first query.
+// vectorsRouter builds the S3 Vectors API router — weed-vector servers
+// register to the master and the backend resolves them lazily, so a server
+// that comes up after the gateway still gets picked up on first query.
 func (s3opt *S3Options) vectorsRouter(s3ApiServer *s3api.S3ApiServer, grpcDialOption grpc.DialOption, masterAddresses []pb.ServerAddress, filerGroup string) *mux.Router {
 	if len(masterAddresses) == 0 {
 		glog.Warningf("S3 Vectors API disabled: no weed-vector registered on master")
@@ -902,10 +902,3 @@ func (v lanceCredentialVendor) VendTableCredentials(ctx context.Context, princip
 		Expiration:      credentials.Expiration,
 	}, nil
 }
-
-// discoverVectorWorker resolves one registered weed-vector server through the
-// master's cluster-nodes list; OSS fans every vector call to that single
-// backend.
-// discoverVectorWorkers returns every registered weed-vector address —
-// callers keep their current worker when it is still listed so
-// membership-order changes cannot churn live connections.