fix(#2962): enable nullglob in for-glob shell blocks for zsh portability (#3087)

* fix(#2962): enable nullglob in for-glob shell blocks for zsh portability

Workflow shell blocks are fenced bash but execute in the user's login shell
(zsh on macOS). zsh's nomatch default aborts the WHOLE block on an unmatched
glob in a for-list (not just skipping the command), silently bypassing every
statement after it — including the verify-phase decision-coverage gate,
whose optional *-CONTEXT.md lookup used the unsafe for-list form so the
DECISION_RESULT= assignment on the next line never ran under zsh.

Fix: prepend a portable nullglob shim to every bash block containing a
for-glob loop:
  shopt -s nullglob 2>/dev/null; setopt NULL_GLOB 2>/dev/null
Each command no-ops (stderr suppressed) in the shell that doesn't recognize
it; the matching shell enables nullglob so an unmatched glob expands to
nothing and the loop body is skipped cleanly. Verified locally: both zsh and
bash now reach end-of-block (rc=0) on a no-match glob; bash matched-case
behavior unchanged.

14 blocks across 7 files: verify-phase.md (4, incl. the decision-coverage
gate), review.md, execute-phase.md, resume-project.md, complete-milestone.md,
audit-milestone.md, gsd-integration-checker.md, gsd-plan-checker.md (3).
Closes the zsh bypass of the #2770 fix.

* chore(#2962): add changeset fragment

* chore(#2962): backfill changeset PR number 3087

---------

Co-authored-by: sim <sim@local>

gsd-core/workflows/execute-phase.md

@@ -1486,12 +1486,13 @@ Copy failure must NOT block phase completion.
 After `update_roadmap`, moves todos whose `resolves_phase` matches to `completed/`.
 
 ```bash
+shopt -s nullglob 2>/dev/null; setopt NULL_GLOB 2>/dev/null
 PHASE_NUM="${PHASE_NUMBER}"
 PENDING_DIR=".planning/todos/pending"
 COMPLETED_DIR=".planning/todos/completed"
 mkdir -p "$COMPLETED_DIR"
 
-# "05"=="5" (#2576).
+#2576
 normalize_phase_num() {
   local p="${1//\"/}"; printf '%s' "$p" | sed 's/^0*\([0-9]\)/\1/'
 }
@@ -1500,7 +1501,6 @@ PHASE_NUM_NORM=$(normalize_phase_num "$PHASE_NUM")
 CLOSED=()
 for TODO_FILE in "$PENDING_DIR"/*.md; do
   [ -f "$TODO_FILE" ] || continue
-  # resolves_phase from first frontmatter block
   RP=$(awk '/^---/{c++;next} c==1 && /^resolves_phase:/{print $2;exit} c==2{exit}' "$TODO_FILE" 2>/dev/null || true)
   RP_NORM=$(normalize_phase_num "$RP")
   if [ -n "$RP_NORM" ] && [ "$RP_NORM" = "$PHASE_NUM_NORM" ]; then