fix(sdd): write artifacts to working-tree .superpowers/sdd, not .git/ (#1780)

skills/subagent-driven-development/scripts/task-brief

@@ -4,8 +4,8 @@
 # through the controller's context.
 #
 # Usage: task-brief PLAN_FILE TASK_NUMBER [OUTFILE]
-# Default OUTFILE: <git-dir>/sdd/task-<N>-brief.md — unique per repo
-# instance, so concurrent sessions cannot collide.
+# Default OUTFILE: <repo-root>/.superpowers/sdd/task-<N>-brief.md
+# (per worktree; concurrent runs in the same working tree share it).
 set -euo pipefail
 
 if [ $# -lt 2 ] || [ $# -gt 3 ]; then
@@ -20,9 +20,7 @@ n=$2
 if [ $# -eq 3 ]; then
   out=$3
 else
-  dir=$(git rev-parse --git-path sdd)
-  mkdir -p "$dir"
-  dir=$(cd "$dir" && pwd)
+  dir=$("$(cd "$(dirname "$0")" && pwd)/sdd-workspace")
   out="$dir/task-${n}-brief.md"
 fi