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/core/system-prompt/README.zh.md

@@ -21,6 +21,8 @@
 - `ctx.systemPrompt.variable(name: string, provider: (context) => string | undefined): () => void`：贡献提示词变量，在段文本中以 `{{name}}` 引用。带作用域变量会为该 agent 遮蔽同名全局变量。同层重复或无法引用的名称会抛出；`undefined` 表示「本次组装没有值」。随调用 fiber 一并 dispose。
 - `ctx.systemPrompt.assemble(context?: AssembleContext): Promise<PromptAssembly>`：为一个调用方组装提示词：将全局层与 `context.scope` 的层合并，并在变换 seam 前分离工具 schema。它经过按作用域筛选的 `system-prompt/assemble` waterfall，并返回其权威结果。可选的 `context.signal` 显式控制本次组装请求；提供方与监听器可以配合该信号，但不得将它保留给另一轮次。当已配置的 `toolOrder` 指名提供方 `knownNames` 全集以外的工具，或提供方返回保留的其余项名称时，调用会被拒绝。
 
+<a id="live-events"></a>
+
 ### 实时事件
 
 `system-prompt/assemble` 是权威来源；替换条目的监听器必须保留任何活动 Code Mode 或结构化输出协议。筛选需要在呈现、查找与执行之间保持一致时，应使用 [`ToolRegistry.restrict()`](../tools/README.md)。注册表变更通知不经过筛选。[system-prompt.md](../../../docs/subsystems/system-prompt.md#cordis-surface) 的生成区块拥有签名与分发契约。