refactor: simplify staged stack configuration

manage.conf

@@ -1,26 +1,14 @@
-# Global maximum number of stacks executed concurrently within a group.
+# Maximum number of stacks executed concurrently within each stage.
 # Use 0 for unlimited concurrency.
-max_parallel 2
+max_parallel 3
 
-# Groups run from top to bottom for up/start/restart/pull/update.
-# They run from bottom to top for stop/down.
-group gateway --parallel 1 \
-	nginx
-
-group network \
-	adguardhome \
-	ddns-go
-
-group services --parallel 3 \
-	samba \
-	immich \
-	gitea \
-	openlist \
-	homeassistant \
-	qbittorrent
-
-group backup --parallel 1 \
-	backrest
+# Each declaration is an ordered stage; stacks on the same line run in parallel.
+# Add --parallel N before the stacks to override max_parallel for that stage.
+# Example: before --parallel 2 stack-a stack-b
+# Unlisted stacks run in the default stage.
+before nginx
+before adguardhome ddns-go
+after backrest
 
 # Excluded stacks are ignored by all bulk commands.
 # exclude experimental-stack