fix(#2431): self-suppress TDD Audit section when all commits are missing (#2467)

* fix(#2431): self-suppress TDD Audit section when all commits are missing

The TDD Audit section in ship.md step 8 was always emitted — but the
execute pipeline only writes gate_status: git trailers when TDD mode is
active. Without TDD mode (the default), every commit's trailer is absent
and the section normalizes to 100% missing, producing a noise table with
no way to disable it.

Fix: add a self-suppress instruction at the point where gate_status
values are normalized. When every commit in the scan normalizes to
'missing', skip both step 8 (TDD Audit section) and step 9 (aggregate
gate_status trailer) entirely. Only emit when at least one commit carries
a real value (skill, fallback, or exempt).

This is data-driven, NOT config-gated. An earlier iteration used inline
'gsd_run query config-get workflow.tdd_mode' — but workflow.tdd_mode is
owned by the tdd capability, and ADR-857 Phase 6 forbids host loop
workflows from reading capability-owned keys via inline config-get. The
self-suppress approach avoids any config-get entirely; it checks the
actual trailer data and skips when there's nothing real to report.

Matches the triage's suggested approach: 'have the audit gracefully
degrade (skip the section)' when there is no real signal.

Tests: tests/workflow-compat.test.cjs gains 3 #2431 assertions:
- documents self-suppress when every commit is missing
- step 9 (aggregate trailer) is also gated on real values existing
- does NOT read workflow.tdd_mode inline (ADR-857 Phase 6 compliant)

The existing feat-41 assertions still pass — the section content is
preserved, only gated by the self-suppress instruction.

References: #2431; PR #585 (consumer shipped, producer never wired);
ADR-857 Phase 6 (capability-owned config keys must not be read inline by
host loop workflows).

* chore(#2431): backfill pr:2467 in .changeset/clever-moles-frolic.md

tests/workflow-size-baseline.json

@@ -71,7 +71,7 @@
   "settings-advanced.md": 40019,
   "settings-integrations.md": 16257,
   "settings.md": 33832,
-  "ship.md": 28310,
+  "ship.md": 28782,
   "sketch-wrap-up.md": 14267,
   "sketch.md": 20369,
   "smart-entry.md": 11489,