The cross-repo gate could never fail the job

`... | tee report.txt` ran under the default shell, which is `bash -e` with
no pipefail, so the step reported tee's exit code. steps.audit.outcome was
success whatever the audit found, the "Fail the job" step never fired, and
the scheduled drift issue could never open.

Proof rather than reasoning: run 30208588762 printed six vocabulary errors
and concluded success. That run is also what surfaced the bug, because it is
the first time this checker had anything to report.

`shell: bash` runs with -eo pipefail, which is the whole fix.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

Author: gift-framework

.github/workflows/cross-repo-consistency.yml

@@ -33,6 +33,11 @@ jobs:
 
       - name: Run cross-repo audit
         id: audit
+        # `shell: bash` is load-bearing: it runs with -o pipefail. The default
+        # shell does not, so `... | tee report.txt` reported tee's exit code and
+        # the audit could never fail the job. Run 30208588762 is the proof: six
+        # vocabulary errors, conclusion success.
+        shell: bash
         run: |
           python3 scripts/arithmon-consistency-check.py \
             --json findings.json | tee report.txt