feat(tool-web): replace the regex HTML-to-markdown converter with turndown

Implements the turndown Agent Note from the NIH dependency audit (full
variant, not the minimal entities-only fallback): dsh-tool-web's fetch
rendering now converts HTML through turndown + @joplin/turndown-plugin-gfm
(atx headings, fenced code, dash bullets, GFM tables/strikethrough) over
the real domino DOM, with script/style/noscript removed wholesale. The
hand-rolled ~86-line regex converter html.ts and its entity tables are
deleted; renderBody wraps the conversion in try/catch falling back to
the raw HTML body, because turndown's recursive DOM walk overflows with
a RangeError on pathological nesting (measured: 4k levels on the main
thread, 8k in a worker) where the regex version could never throw.

Closure weight, measured: tool-web IS in the single-exe runtime closure,
and the exe asset globs would pack ~7.9 MB of the three new packages —
but ~6 MB of that is domino's test corpus, with runtime lib/ at ~550 KB
against a ~174 MB artifact (<0.5% either way), so the swap wins.

Per testing policy the previously-missing keyless web_fetch snapshot
ships in the same change: the acp-agent `web-fetch` scenario boots a new
web.cordis.yml overlay (web seam + real dsh-web-fetch-local provider +
tool-web fetch-only + a loopback HTTP fixture server on a fixed port
serving deterministic HTML with entities, a GFM table, and nesting), so
recording and keyless replay both drive the real HTTP fetch and real
conversion end to end; the scenario pins the new `web` header class.

The Agent Note moves proposed -> implemented and is rewritten per the
lifecycle contract (Decision/Consequences/Testing, closure verdict and
alternatives recorded); tool-web and acp-agent READMEs updated in both
languages and pairs re-recorded.

examples/acp-agent/README.zh.md

@@ -9,7 +9,7 @@ pnpm run demo:acp             # needs DEEPSEEK_API_KEY (repo-root .env or env)
 pnpm run demo:code-mode acp   # same protocol with the Code Mode tool transport
 ```
 
-该叶节点加载 ACP 应用、DeepSeek 适配器、受沙箱限制的 bash 与文件系统栈、一次性批准策略、压缩（compaction）、subagent、工作流、钩子、派生会话查询索引和重复守卫。应用为每次 `session/new` 创建一个新 agent，将会话持久化到 JSONL，并保持 stdout 只含协议内容。[`session-query.cordis.yml`](session-query.cordis.yml) 为其专用快照显式选用 workspace 授权的查询工具和通用超时／溢出策略；[`fs.cordis.yml`](fs.cordis.yml) 为文件系统场景添加溢出存储，[`code-mode.cordis.yml`](code-mode.cordis.yml) 则添加 `run_code` 及其生成的 TypeScript SDK。
+该叶节点加载 ACP 应用、DeepSeek 适配器、受沙箱限制的 bash 与文件系统栈、一次性批准策略、压缩（compaction）、subagent、工作流、钩子、派生会话查询索引和重复守卫。应用为每次 `session/new` 创建一个新 agent，将会话持久化到 JSONL，并保持 stdout 只含协议内容。[`session-query.cordis.yml`](session-query.cordis.yml) 为其专用快照显式选用 workspace 授权的查询工具和通用超时／溢出策略；[`fs.cordis.yml`](fs.cordis.yml) 为文件系统场景添加溢出存储，[`code-mode.cordis.yml`](code-mode.cordis.yml) 添加 `run_code` 及其生成的 TypeScript SDK，[`web.cordis.yml`](web.cordis.yml) 则为 web-fetch 快照添加 web seam、本地抓取提供方、`web_fetch` 与一个回环 HTML fixture 服务器。
 
 ## 协议通道