feat: accept stack folders as stack arguments

Folder references like qbittorrent/ or ./qbittorrent/ now select the
same stack as the bare name, which matches shell tab completion.
Paths are resolved against the stacks root and must point at a stack
folder inside STACKS_DIR; folders elsewhere are rejected before any
Docker command runs.

manage.sh

@@ -71,6 +71,10 @@ usage() {
 	cat <<EOF
 Usage: $(basename "$0") COMMAND [STACK]
 
+STACK may be a plain stack name or a stack folder such as qbittorrent/
+or ./qbittorrent/. Folder references resolve against the stacks root;
+paths outside it are rejected.
+
 Lifecycle:
   up [STACK]       Create and start containers
   start [STACK]    Start existing containers
@@ -155,6 +159,42 @@ validate_name() {
 		die "invalid $kind name: $value"
 }
 
+# Rewrite a stack argument to its bare stack name in place. Plain names
+# pass through unchanged. A folder reference such as ./stack/ or an
+# absolute path must resolve, after following symlinks, to the stack
+# folder inside STACKS_DIR; paths to folders elsewhere are rejected.
+normalize_target() {
+	local target_name="$1"
+	local -n target="$target_name"
+	local original="$target"
+	local name path resolved canonical root
+
+	while [[ "$target" == */ ]]; do
+		target="${target%/}"
+	done
+
+	# Names without a path component are validated against the stacks.
+	if [[ "$target" != */* ]]; then
+		[[ -n "$target" ]] || die "invalid stack path: $original"
+		return 0
+	fi
+
+	name="${target##*/}"
+	[[ -n "$name" ]] || die "invalid stack path: $original"
+	root="$(readlink -f -- "$STACKS_DIR" 2>/dev/null)" ||
+		die "invalid STACKS_DIR: $STACKS_DIR"
+	path="$target"
+	[[ "$path" == /* ]] || path="$STACKS_DIR/$path"
+	resolved="$(readlink -f -- "$path" 2>/dev/null)" ||
+		die "stack folder not found: $original"
+	[[ -d "$resolved" ]] || die "stack folder not found: $original"
+	canonical="$(readlink -f -- "$root/$name" 2>/dev/null)"
+	[[ "$resolved" == "$canonical" ]] ||
+		die "not a stack folder in $root: $original"
+
+	target="$name"
+}
+
 # Set the maximum concurrency within each stage.
 max_parallel() {
 	[[ $# -eq 1 ]] || die "max_parallel expects exactly one value"
@@ -170,6 +210,7 @@ add_stage() {
 	local stack
 	local -n stages="$stages_name"
 	local -n limits="$limits_name"
+	local -a normalized=()
 	shift 3
 
 	if [[ "${1:-}" == "--parallel" ]]; then
@@ -182,15 +223,17 @@ add_stage() {
 	[[ $# -ge 1 ]] || die "$stage expects at least one stack"
 
 	for stack in "$@"; do
+		normalize_target stack
 		validate_name "stack" "$stack"
 		contains "$stack" "${CONFIGURED_STACKS[@]}" &&
 			die "stack is assigned more than once: $stack"
 		contains "$stack" "${EXCLUDED_STACKS[@]}" &&
 			die "stack is both assigned and excluded: $stack"
 		CONFIGURED_STACKS+=("$stack")
+		normalized+=("$stack")
 	done
 
-	stages+=("$*")
+	stages+=("${normalized[*]}")
 	limits+=("$limit")
 }
 
@@ -203,6 +246,7 @@ exclude() {
 
 	local stack
 	for stack in "$@"; do
+		normalize_target stack
 		validate_name "stack" "$stack"
 		contains "$stack" "${EXCLUDED_STACKS[@]}" &&
 			die "stack is excluded more than once: $stack"
@@ -707,6 +751,10 @@ main() {
 		;;
 	esac
 
+	if [[ -n "$TARGET" ]]; then
+		normalize_target TARGET
+	fi
+
 	load_config
 	discover_stacks
 	validate_config_stacks