refactor(completion): name path arguments explicitly and share firstArg

The six commands that take a file or directory argument set their
completer directly instead of a Use-line parser wrapping every
command, the first-argument-only wrappers become one firstArg helper,
and only the bash completion help keeps a custom text.

Signed-off-by: bircni <bircni@icloud.com>

internal/app/artifacts.go

@@ -50,7 +50,7 @@ $ tea run artifact list 34`,
 		},
 	}
 	pageFlags(list, &limit, &page)
-	list.ValidArgsFunction = a.completeRunArg()
+	list.ValidArgsFunction = firstArg(a.completeRuns())
 	group.AddCommand(list)
 
 	return group
@@ -148,7 +148,7 @@ $ tea run download 34 --zip`,
 	destination.register(cmd)
 	cmd.Flags().StringSliceVarP(&names, "name", "n", nil, "Only download the artifacts with these names")
 	cmd.Flags().BoolVar(&asZip, "zip", false, "Save each artifact as a ZIP archive instead of extracting it")
-	cmd.ValidArgsFunction = a.completeRunArg()
+	cmd.ValidArgsFunction = firstArg(a.completeRuns())
 	_ = cmd.RegisterFlagCompletionFunc("name", commaSeparated(a.completeArtifactNames()))
 	return cmd
 }