docs(bench): redact real ssh port in methodology SVG and markdown

Replace the literal source port (a real ssh port previously used in
internal infrastructure) with an unambiguous placeholder so the
artifact contains zero recognizable production-side values.

Files changed:
- cvm-bench-methodology.svg
- cvm-bench-methodology.md

Substitution:
- :<real-port> -> :22  becomes
  :<actual-ssh-port> -> :22

The placeholder is rendered in SVG with HTML entity escapes
(&lt; / &gt;) so it shows as <actual-ssh-port> in any browser without
breaking SVG well-formedness. Markdown uses the angle-bracket form
verbatim as part of the sample sed command, alongside an existing
note that the regex must be substituted with the real value at
invocation time.

Rationale: paired with the earlier IP D-segment-only redaction, this
ensures the methodology document keeps zero real network identifiers
visible while still conveying the redaction pipeline structure to the
reader.

Author: jfb8856606

docs/freebsd_13_to_15_upgrade_spec/zh_cn/cvm-bench-methodology.md

@@ -110,7 +110,7 @@ ssh 回流的 stdout 在写入工件前由 AI AGENT 的 sed 管道完成混淆
 | sed -e 's/x\.x\.x\.176/192.168.1.1/g' \
       -e 's/x\.x\.x\.67/192.168.1.2/g' \
       -e 's/x\.x\.x\.87/192.168.1.3/g' \
-      -e 's/:36000/:22/g'
+      -e 's/:<实际ssh端口>/:22/g'
 ```
 > 此处 `x.x.x.176` 为占位写法表示真实 A/B/C 段被屏蔽、仅保留 D 段；实际命令中需替换成真实正则。
 > `perf.data` 二进制不修改（信息密度低、可读性差，对外部信息泄漏风险极小）。