Allow dots in app names (closes #260)

App names may now contain dots, such as sneak.berlin: runs of
lowercase letters and numbers joined by single dots or by hyphens,
2 to 63 characters. Docker accepts every such name in the app's image
name, upaas-<name>; a dot needs a letter or number on both sides
because Docker requires it. The rule also keeps a dot off either end,
so the name is safe as a directory and log file name.

The new and edit app forms use the same pattern. Their old one was not
a valid regular expression under the flag browsers compile it with, so
browsers ignored it.

Model: opus-5-5

go.mod

@@ -4,6 +4,7 @@ go 1.25
 
 require (
 	github.com/99designs/basicauth-go v0.0.0-20230316000542-bf6f9cbbf0f8
+	github.com/distribution/reference v0.6.0
 	github.com/docker/docker v27.3.1+incompatible
 	github.com/docker/go-connections v0.6.0
 	github.com/go-chi/chi/v5 v5.2.3
@@ -39,7 +40,6 @@ require (
 	github.com/containerd/ttrpc v1.2.5 // indirect
 	github.com/containerd/typeurl/v2 v2.2.0 // indirect
 	github.com/davecgh/go-spew v1.1.1 // indirect
-	github.com/distribution/reference v0.6.0 // indirect
 	github.com/docker/go-units v0.5.0 // indirect
 	github.com/felixge/httpsnoop v1.0.4 // indirect
 	github.com/fsnotify/fsnotify v1.9.0 // indirect