Fix what the Go 1.26 language bump breaks (#10794)

* worker: log the balance move stage through a constant format string

Go 1.26's printf analyzer now follows printf wrappers reached through an
interface, so passing the stage straight to Logger.Info is a vet failure.

* s3api: bracket the IPv6 host in the signature test URL

A bare IPv6 literal is legal in a Host header but never in a URL. Go 1.26
stopped parsing it leniently, so carry the two forms separately and set
r.Host to the value the client would actually have signed.

* mini: bracket IPv6 addresses in the readiness probe URLs

An IPv6-only host hands mini a bare literal, and %s:%d pasted it into a URL
unbracketed. Under Go 1.26 that URL no longer parses, so waiting for the
admin server never succeeds and mini refuses to start.

weed/worker/tasks/balance/balance_task.go

@@ -81,7 +81,7 @@ func (t *BalanceTask) Execute(ctx context.Context, params *worker_pb.TaskParams)
 		IoBytePerSecond: balanceParams.IoBytePerSecond,
 		Progress: func(percent float64, stage string) {
 			t.ReportProgress(percent)
-			t.GetLogger().Info(stage)
+			t.GetLogger().Info("move stage: %s", stage)
 		},
 	})
 	if err != nil {