blog: add APISIX throughput regression investigation (en + zh)

[Yilialinn]

Summary

• add the Simplified Chinese APISIX throughput-regression investigation and its English counterpart
• adapt the English article from the current Chinese source for natural developer-facing English while preserving the same technical facts, data, code, tables, images, limitations, and four references
• use the shorter English title “APISIX Throughput Regression: Beyond the Flame Graph” and remove literal or editor-sounding phrasing from the English article
• address all eight English review comments, including the opening, CPU prerequisite, LuaJIT wording, summary table, conclusion language, and canonical English reference titles
• run a final bilingual wording pass to remove vague value metaphors, editor voice, and literal phrasing while preserving the technical facts and causal boundaries
• align both locales after the latest Chinese edits, including clearer metric denominators, flame-graph attribution limits, normalized-throughput wording, and complete bilingual figure captions
• keep technical corrections outside the source article’s scope; do not add PR #13779, release/version notes, or separate LuaJIT corrections

Review focus

• treat blog/zh/blog/2026/08/28/debugging-apisix-throughput-regression.md as the technical source for this PR
• review blog/en/blog/2026/08/28/debugging-apisix-throughput-regression.md for natural developer-facing flow and semantic fidelity, rather than sentence-by-sentence literal parity
• both locales contain the same 6 H2 sections, 3 H3 sections, 5 tables, 3 Lua code blocks, 2 images, and 4 references
• this final wording pass updates both locales; review the diff for direct, natural developer-facing phrasing and conservative causal claims

Validation

• lightweight YAML frontmatter parsing on both articles
• CI-version markdownlint-cli@0.25.0 on both articles
• bilingual checks confirm matching structure, URLs, inline technical tokens, executable code, and numeric values
• git diff --check
• independent final review after fixes: no remaining P0-P2 findings
• full repository Remark/frontmatter checks and site build not rerun locally because node_modules is unavailable; remote CI will validate the new head

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