fix GitHub Pages build

[LjyYano]

What changed

• split two compound where_exp expressions into Liquid 4-compatible chained filters
• remove the unused README navigation Python script and its GitHub Actions workflow
• remove obsolete README maintenance instructions and generated-region markers while keeping the current article navigation

Root cause

GitHub Pages uses Jekyll 3.10 with Liquid 4.0.4. Its where_exp parser accepts one comparison per expression, so the compound and expressions failed during the Pages build.

Validation

• reproduced the original failure with Liquid 4.0.4 parsing rules
• confirmed both replacement expressions parse successfully
• checked the repository for remaining compound where_exp expressions and removed script references
• git diff --check passes

[chatgpt-codex-connector]

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[chatgpt-codex-connector]

Preserve updates for the README article index

When a new article Markdown file is pushed, removing this trigger together with scripts/update_readme_nav.py leaves no repository-wide replacement that updates the static README navigation. The README still presents that section as “全部文章”/“完整文章导航”, so after the next article is added the repository front page will silently omit it; retain an update mechanism or stop presenting the retained static list as complete.

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