CI: fix parallel-install gate ref check (--end-of-options, not --)

The TASK-044 v1+v2 parallel-install gate always false-SKIPped with
"ref 'origin/master' not in this repository" even though the CI step
successfully fetches origin/master. Cause: the Phase-2 ref probe used
`git rev-parse --verify -- "$MASTER_REF"`. The `--` makes rev-parse treat
the following argument as a PATHSPEC, not a revision, so it never resolved
the ref (verified locally: `rev-parse --verify -- origin/master` fails,
`rev-parse --verify origin/master` succeeds). Since skip is not authorized
in CI, the gate failed the gcc-14 dynamic lane on every run.

Use `--end-of-options`, which ends option parsing (preserving the guard
against an option-like MASTER_REF) while still treating the argument as a
revision. Line 176's `worktree add` takes the ref as a trailing positional
and is unaffected.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01NpysYDDJac63yz2mZKKiDf

Author: etr

scripts/check-parallel-install.sh

@@ -160,7 +160,11 @@ pass "v2 install succeeded into $SHARED_STAGE"
 # ---- Phase 2: materialise v1 source via git worktree --------------------------
 echo "Phase 2: building $MASTER_REF in a temporary git worktree"
 
-if ! git -C "$REPO_ROOT" rev-parse --verify -- "$MASTER_REF" >/dev/null 2>&1; then
+# `--end-of-options` (not `--`) guards against an option-like MASTER_REF while
+# still treating it as a revision: `rev-parse --verify -- <ref>` interprets the
+# arg after `--` as a PATHSPEC, so it never resolves the ref and the gate always
+# false-SKIPped ("ref not in this repository") even when origin/master was fetched.
+if ! git -C "$REPO_ROOT" rev-parse --verify --end-of-options "$MASTER_REF" >/dev/null 2>&1; then
     skip_or_fail "ref '$MASTER_REF' not in this repository — cannot do automated v1 build"
 fi