Use Unix sockets for gRPC in mini mode (#8856)

* Use Unix sockets for gRPC between co-located services in mini mode

In `weed mini`, all services run in one process. Previously, inter-service
gRPC traffic (volume↔master, filer↔master, S3↔filer, worker↔admin, etc.)
went through TCP loopback. This adds a gRPC Unix socket registry in the pb
package: mini mode registers a socket path per gRPC port at startup, each
gRPC server additionally listens on its socket, and GrpcDial transparently
routes to the socket via WithContextDialer when a match is found.

Standalone commands (weed master, weed filer, etc.) are unaffected since
no sockets are registered. TCP listeners are kept for external clients.

* Handle Serve error and clean up socket file in ServeGrpcOnLocalSocket

Log non-expected errors from grpcServer.Serve (ignoring
grpc.ErrServerStopped) and always remove the Unix socket file
when Serve returns, ensuring cleanup on Stop/GracefulStop.

weed/admin/dash/worker_grpc_server.go

@@ -108,6 +108,8 @@ func (s *WorkerGrpcServer) StartWithTLS(port int) error {
 	go s.cleanupRoutine()
 	go s.activeLogFetchLoop()
 
+	pb.ServeGrpcOnLocalSocket(grpcServer, port)
+
 	// Start serving in a goroutine
 	go func() {
 		if err := s.grpcServer.Serve(listener); err != nil {