refactor: dedupe theme values and app helpers

apps/apply

@@ -2,18 +2,8 @@
 
 use ./common.nu *
 
-def get-hostname [] {
-	if $nu.os-info.name == "macos" {
-		try { ^scutil --get LocalHostName | str trim } catch { ^hostname -s | str trim }
-	} else {
-		^hostname | str trim
-	}
-}
-
 def main [hostname?: string, ...rest: string] {
-	let host = if ($hostname | is-empty) {
-		get-hostname
-	} else { $hostname }
+	let host = resolve-host $hostname
 
 	print_info $"Applying configuration for ($host)"