fix(sdd): invoke sdd-workspace via bash so helpers survive stripped exec bits

Codex marketplace users hit 'Permission denied' running SDD helpers:
some extractors (Python zipfile) discard Unix mode attributes when
unpacking the package, so task-brief's and review-package's direct exec
of their sibling sdd-workspace fails. Our packaging preserves 0755
(git archive | tar -xpf, asserted by the existing packaging test) — the
bits are lost on the consumer side, which no packaging change can reach.
Invoking the sibling via "${BASH:-bash}" makes the exec bit irrelevant.

TDD: new regression case copies the helpers, chmod -x, runs task-brief
via bash — RED with the reported rc=126 Permission denied, GREEN after.

Reported in #2040 (michaelholcomb-creator). Fixes #2040.

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

@@ -21,7 +21,9 @@ n=$2
 if [ $# -eq 3 ]; then
   out=$3
 else
-  dir=$("$(cd "$(dirname "$0")" && pwd)/sdd-workspace" "$plan")
+  # Invoke via bash rather than direct exec: some extractors (Python zipfile)
+  # strip Unix exec bits when unpacking marketplace packages (#2040).
+  dir=$("${BASH:-bash}" "$(cd "$(dirname "$0")" && pwd)/sdd-workspace" "$plan")
   out="$dir/task-${n}-brief.md"
 fi