feat: Add the vantagectl module and its cobra root

Its own module rather than a package under shared, so cobra and pflag stay
out of the module graphs of server, admin and sitesvc, which never use
them.

go.mod

@@ -0,0 +1,23 @@
+module gitea.hostxtra.co.uk/mrhid6/vantage/vantagectl
+
+go 1.26
+
+replace gitea.hostxtra.co.uk/mrhid6/vantage/shared => ../shared
+
+require (
+	github.com/spf13/cobra v1.10.2
+	go.mongodb.org/mongo-driver/v2 v2.8.0
+)
+
+require (
+	github.com/inconshreveable/mousetrap v1.1.0 // indirect
+	github.com/klauspost/compress v1.17.6 // indirect
+	github.com/spf13/pflag v1.0.9 // indirect
+	github.com/xdg-go/pbkdf2 v1.0.0 // indirect
+	github.com/xdg-go/scram v1.2.0 // indirect
+	github.com/xdg-go/stringprep v1.0.4 // indirect
+	github.com/youmark/pkcs8 v0.0.0-20240726163527-a2c0da244d78 // indirect
+	golang.org/x/crypto v0.33.0 // indirect
+	golang.org/x/sync v0.11.0 // indirect
+	golang.org/x/text v0.22.0 // indirect
+)