Enhancement(#41): /gsd-ship extracts per-commit gate_status into a PR-body TDD Audit + squash trailer (#585)

* feat(#41): extract per-commit gate_status into ship PR body TDD Audit

/gsd:ship's generate_pr_body now reconstructs the TDD gate trail that a
squash-merge would otherwise discard. A new TDD Audit section walks the
merge-base..HEAD commit range (merges excluded), reads each commit's
gate_status: trailer via Git's native trailer machinery, pairs each
test: commit with its following feat:/fix: implementation commit, and
counts commits lacking a recognized trailer as missing. A single
aggregate `gate_status: skill=N, fallback=N, exempt=N, missing=N`
trailer is emitted as the final line of the PR body so a GitHub
squash-merge carries the audit footprint into the base branch.

Hardening (per adversarial review): impl pairing is restricted to
feat:/fix: (refactor/docs/chore are skipped, never mistaken for GREEN);
the gate_status cell is normalized to a known token and never rendered
raw; commits with multiple gate_status trailers are treated as missing;
every table cell escapes pipes and strips CR/LF; records guard against
delimiter-injection from adversarial commit messages.

Scoped additively: no changes to commands, agents, templates, or SDK.

Closes #41

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

* docs(#41): add changeset for ship TDD Audit enhancement

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

---------

Co-authored-by: Claude Opus 4.8 <noreply@anthropic.com>

docs/ship-pr-body-sections.md

@@ -13,8 +13,19 @@ Every generated `/gsd-ship` PR body keeps the required core sections:
 - `Requirements Addressed`
 - `Verification`
 - `Key Decisions`
+- `TDD Audit`
 
-Custom sections are append-only. They render after `Key Decisions`; they cannot replace, remove, or reorder the core sections.
+Custom sections are append-only. They render after `Key Decisions` (and before the `TDD Audit`); they cannot replace, remove, or reorder the core sections.
+
+### TDD Audit section
+
+The `TDD Audit` section is always appended last. It walks the commits in the `merge-base..HEAD` range (merges excluded), reads each commit's `gate_status:` Git trailer (`skill` | `fallback` | `exempt`), and pairs each `test:` commit with its following `feat:`/`fix:` implementation commit in a table. Commits that carry no recognized trailer are counted as `missing`.
+
+The section closes with a single aggregate trailer line that a GitHub squash-merge carries into the base branch:
+
+```
+gate_status: skill=3, fallback=1, exempt=0, missing=0
+```
 
 ## Configure Sections During Onboarding