use the real module path

The module was code.aneur.in/cloud/ultrashorty but go.mod (and main.go's
internal import) still said gogs.home.aneur.in/go/ultrashorty, a host that
no longer exists. Self-consistent so it built, but wrong for anyone
fetching it and confusing to read.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

main.go

@@ -6,7 +6,7 @@ import (
 
 	"github.com/alecthomas/kong"
 	"github.com/rs/zerolog"
-	"gogs.home.aneur.in/go/ultrashorty/internal"
+	"code.aneur.in/cloud/ultrashorty/internal"
 )
 
 func main() {