cmd/app: use ROSA_ prefix

This avoids awkward case-insensitive zsh completion.

Signed-off-by: Ophestra <cat@gensokyo.uk>

cmd/app/main.go

@@ -59,7 +59,7 @@ func main() {
 		"Increase log verbosity",
 	).Flag(
 		&flagBase,
-		"d", command.StringFlag("$HAKUREI_APP_PATH"),
+		"d", command.StringFlag("$ROSA_APP_PATH"),
 		"Configuration and state directory",
 	)