fix(tool-web): bound conversion depth and complete fetch output

Two review findings on the turndown swap, both verified empirically:

- Unclosed-tag nesting makes the synchronous turndown/domino walk
  superlinear (measured: depth 512 ~0.15s, 2k ~2s, 20k ~5s), during
  which the cooperative fetchTimeoutMs timer cannot fire. renderBody
  now preflights nesting depth with a linear tag scan and passes
  bodies past 512 levels through raw; the try/catch stays for markup
  the scan cannot see (comment-hidden tags), simulated in tests via a
  converter throw.
- Markdown escaping can expand converted HTML ~2x (100k underscores
  render as 200k chars), so provider body caps no longer bounded the
  model-visible result. formatFetchOutput now caps the complete output
  (header + body + footer) under new fetchMaxOutputChars config
  (default 200000 = 2x the local provider's default body cap), reusing
  the truncation notice.

README EN+ZH, config catalog, Agent Note EN+ZH updated; the new
web-fetch fixture is migrated to the packed layout master now
requires; tool-web coverage stays 100% per-file.

docs/config-catalog.md

@@ -1656,7 +1656,7 @@ Source: [`packages/tasks/tool-tasks/src/index.ts:23`](../packages/tasks/tool-tas
 Requires: `tools` · `web` · `systemPrompt`
 
 ```ts config-catalog
-/** Plugin config: which web tools to register, the source cap, and per-tool budgets. */
+/** Plugin config: which web tools to register, the source cap, per-tool budgets, and the fetch output cap. */
 export interface Config {
   /** Register `web_search`. Defaults to true. */
   search?: boolean
@@ -1668,10 +1668,12 @@ export interface Config {
   fetchTimeoutMs?: number
   /** Cooperative timeout budget (ms) for `web_search`. Defaults to 30000. */
   searchTimeoutMs?: number
+  /** Cap on one `web_fetch` output's characters (header, rendered body, and footer). Defaults to 200000. */
+  fetchMaxOutputChars?: number
 }
 ```
 
-Source: [`packages/web/tool-web/src/index.ts:28`](../packages/web/tool-web/src/index.ts)
+Source: [`packages/web/tool-web/src/index.ts:37`](../packages/web/tool-web/src/index.ts)
 
 ## `@deepseek-ai/dsh-tool-workflow`