docs,feat(doc-gates): fix 15 dead anchor fragments; verify-md-links now validates fragments

A corpus sweep under the doc/prose standards found 15 links whose #fragment
named no anchor in its target — reworded headings, one relocated contract
(tool-fs → the group README's no-timeout rule), and zh sides citing English
slugs their Chinese headings never produce. Fixed all 15 (zh sides get the
conventional explicit <a id> + English fragment), fixed the one generator-owned
instance at its source (gen-doc-graphs), and extended verify-md-links to
resolve fragments onto Markdown targets — same-file anchors included — against
heading slugs and explicit <a id>, so the class is gated instead of manually
grepped. Remaining probes (narrated history, duplication shingles, comment
transcripts, budgets) came back clean; sibling-adapter README symmetry and
implemented-note contrasts are deliberate keeps.

packages/credentials/credentials-local/README.i18n.yaml

@@ -3,4 +3,4 @@
 # after editing either side, bring the other along and re-record with:
 #   pnpm run verify-translation-pairing --write packages/credentials/credentials-local/README.md
 README.md: 6051c07628c0214f9396d12554719c5614610826
-README.zh.md: c6f3901af925d4bd31d2dcfbf5f5f65de62dac81
+README.zh.md: 23f48080136b5d212bef34d931a74773c5da4fd3

packages/credentials/credentials-local/README.zh.md

@@ -49,6 +49,8 @@ OPENAI_API_KEY: sk-…
 
 外部编辑在快照**整体替换**后按变更引用逐个发布 `credentials/updated`——磁盘上删掉的条目绝不在内存滞留。提供方自己的写入按内容识别，只发布属于该次提交的一个事件。运行期文档不可读或无效时保留最后可用快照并告警；文件不存在即空存储；启动时不可读或无效则明确报错。
 
+<a id="security-boundary"></a>
+
 ## 安全边界
 
 文档在 `0700` 目录下以 `0600` 权限存放，这挡得住其他 OS 用户，**挡不住**模型。工具进程（bash、文件系统工具）以同一用户身份运行，而已交付的 `workspace-write` 文件策略限制的是修改而非读取，因此它们读这个文件与读该用户拥有的任何其他文件毫无二致；也没有任何沙箱模式会把它单独挑出来。harness 真正守住的更窄：它绝不把该文档的解析后路径交给模型，也绝不把它载入进程环境——这与用户的普通环境层 `$DSH_HOME/.env` 不同（见 [app-boot 的 Harness home 各层](../../boot/app-boot/README.md#profiles)）——因此要拿到这个值，需要刻意去读一条并未交给 agent（智能体）的路径。