docs: add 10-pg_clean.en.md English translation

[Lycorius03]

What

Adds the missing English page docs/guide/10-pg_clean.en.md, i.e. the English translation of docs/guide/10-pg_clean.md.

Related issue: OpenTenBase/OpenTenBase#40

Why

The documentation site is bilingual, driven by mkdocs-static-i18n with docs_structure: suffix in mkdocs.yml. When a page has no .en.md sibling, the English build falls back to the Chinese source. So right now:

Page	CJK characters in the rendered page	Meaning
/en/guide/10-pg_clean/	499	body is still Chinese
/guide/10-pg_clean/	741	Chinese page (expected)
/en/guide/11-pg_unlock/	42	already translated — navigation only

Meanwhile the navigation entry in mkdocs.yml (nav_translations) already reads V2.3.0 Feature pg_clean, so the English page has an English title over Chinese body text. The only thing missing is this file.

Scope

One new file, added only. No existing file is modified.

Four earlier attempts on the same file did not land, so it is worth being explicit about what this PR deliberately does not do:

• #28 edited the Chinese source 10-pg_clean.md (+61 −70) instead of adding the .en.md file;
• #5 added this page but also carried an unrelated one-line change to 02-access.md and a second, unrelated new page (09-problem-performance.en.md) that still had unresolved review comments — that second file is what held the whole PR.

This PR keeps the diff to a single added file so it can be reviewed and merged on its own.

Checklist

• Filename follows the i18n suffix convention: 10-pg_clean.en.md
• LF line endings
• Both image references preserved — images/v.2.3.0_pg_clean_check_txn.png and images/v2.3.0_pg_clean_execute.png, both already present in the repo
• Section structure, code blocks and command outputs unchanged from the Chinese source
• Terminology unified on "residual" for 残留
• CLA signed

Note: the issue is filed in OpenTenBase/OpenTenBase, so GitHub will not close it automatically from this repository — it needs to be closed manually once this PR is merged.

[CLAassistant]

All committers have signed the CLA.

[Lycorius03]

Ready for review — both required checks are green:

• license/cla — signed
• GITHUB_OPENSOURCE_SCAN_PIPELINE@PULL_REQUEST — pass (2m18s)

The diff is a single added file, docs/guide/10-pg_clean.en.md (+70 / −0). No existing file is modified, and mkdocs.yml is untouched — nav_translations already contains the entry for this page, so the file is the only missing piece.

I kept it to one file on purpose. #5 covered this same page but also carried an unrelated 02-access.md edit and a second new page with unresolved review comments, which is what held the whole PR; #28 edited the Chinese source instead of adding the English file.

One note for whoever merges: the issue (OpenTenBase/OpenTenBase#40) lives in the main repository, so GitHub will not close it from here — it needs a manual close.

Happy to adjust the wording anywhere if you'd like a different phrasing for 残留 or the section titles.

[Lycorius03]

说的都队