fix(#2767): pass paths via --files to gsd-sdk query commit + lint guard (#2781)

* fix(#2767): pass paths via --files to gsd-sdk query commit + lint guard

Workflows, agents, commands, and references passed file paths positionally
to `gsd-sdk query commit`, which silently appended them to the commit
subject and triggered the `.planning/` wholesale-stage fallback in
sdk/src/query/commit.ts:136. Regression of #733/#798.

Inserted `--files` before the path list at every site (81 invocations
across 50 files). Added tests/bug-2767-gsd-sdk-commit-files-flag.test.cjs
as a permanent lint that scans every shipped .md file and asserts each
`gsd-sdk query commit[-to-subrepo]` invocation either uses `--files` or
carries no path arguments.

Closes #2767

* test(#2767): replace source-grep with behavioral SDK test

The original test walked every shipped .md file and regex-tokenized
`gsd-sdk query commit` invocations to assert `--files` was present.
CONTRIBUTING.md prohibits this source-grep pattern.

Rewrite as behavioral SDK tests against `sdk/dist/cli.js` over a real
tmp git project (createTempGitProject helper). Cover both the
well-formed (`--files <paths>`) form — clean subject, exactly-staged
files, .planning/ left untouched — and the buggy positional form,
asserting the documented misbehavior (paths leak into subject + the
`.planning/` wholesale-stage fallback at commit.ts:136). Also asserts
`commit-to-subrepo` rejects when `--files` is omitted (commit.ts:258).

The doc-lint is retained as a supplementary defense-in-depth guard
since agent-prompt markdown invocations cannot be exercised end-to-end
— but it is no longer the primary contract.

* docs(#2767): correct contradictory --files guidance in zh-CN/en docs + fix test docstring

commands/gsd/add-backlog.md

@@ -54,7 +54,7 @@ the normal phase sequence and accumulate context over time.
 
 5. **Commit:**
    ```bash
-   gsd-sdk query commit "docs: add backlog item ${NEXT} — ${ARGUMENTS}" .planning/ROADMAP.md ".planning/phases/${NEXT}-${SLUG}/.gitkeep"
+   gsd-sdk query commit "docs: add backlog item ${NEXT} — ${ARGUMENTS}" --files .planning/ROADMAP.md ".planning/phases/${NEXT}-${SLUG}/.gitkeep"
    ```
 
 6. **Report:**

commands/gsd/review-backlog.md

@@ -47,7 +47,7 @@ milestone sequence or remove stale entries.
 
 6. **Commit changes:**
    ```bash
-   gsd-sdk query commit "docs: review backlog — promoted N, removed M" .planning/ROADMAP.md
+   gsd-sdk query commit "docs: review backlog — promoted N, removed M" --files .planning/ROADMAP.md
    ```
 
 7. **Report summary:**

commands/gsd/thread.md

@@ -83,7 +83,7 @@ When SUBCMD=close and SLUG is set (already sanitized):
 
 3. Commit:
    ```bash
-   gsd-sdk query commit "docs: resolve thread — {SLUG}" ".planning/threads/{SLUG}.md"
+   gsd-sdk query commit "docs: resolve thread — {SLUG}" --files ".planning/threads/{SLUG}.md"
    ```
 
 4. Print:
@@ -191,7 +191,7 @@ updated: {today ISO date}
 
 5. Commit:
    ```bash
-   gsd-sdk query commit "docs: create thread — ${ARGUMENTS}" ".planning/threads/${SLUG}.md"
+   gsd-sdk query commit "docs: create thread — ${ARGUMENTS}" --files ".planning/threads/${SLUG}.md"
    ```
 
 6. Report: