Complete Chinese and English research URL localization

[floatingCatty]

SEO decision: separate only genuinely bilingual, substantive research content

Google advises one crawlable URL per language when the main page content actually differs. Building English and Chinese clones for an English-only journal abstract or an untranslated essay is not useful.

This PR completes the 2026 research-note localization pilot without changing any original research URL:

Content	Existing English URL	Added complete Chinese URL
AD-NEGF	/research/ad-negf/	/zh/research/ad-negf/
DeePTB-NEGF	/research/deeptb-negf/	/zh/research/deeptb-negf/
FeRh	/research/ferh-magnetism/	/zh/research/ferh-magnetism/
LogDet	/research/logdet-entropy/	/zh/research/logdet-entropy/
Moiré phonons	/research/moire-phonon/	/zh/research/moire-phonon/
Neural quantum states	/research/nqs-impurity/	/zh/research/nqs-impurity/
SLEM	/research/slem/	/zh/research/slem/
VBCSR	/research/vbcsr/	/zh/research/vbcsr/

DeePTB and flower were already converted in PR #5. After this PR all ten research/software notes have localized English and Chinese addresses.

• Identical prose to the original approved versions, moved into single-language pages. No keyword stuffing or invented translations.
• Retain original English URL and provide a Chinese URL with independent self-canonical, hreflang, html lang, language-appropriate title/description, and accurate per-page BlogPosting inLanguage.
• Add a fully localized /zh/research/ index linking statically to Chinese articles, while the original /research/ index becomes English-only. Both indexes have reciprocal hreflang and visible language links. This does not rely on JavaScript for discovery.
• The shared navigation uses a locale-appropriate research/About link, plus data-href support for bilingual legacy pages.
• The existing /research.json already deduplicates translation_of records and includes both URL versions. The rendered-site audit already asserts reciprocal links, canonicals and per-language article bodies.

Intentionally not copied: Individual paper pages are official English-language publication data; copies with the same English abstract would be thin near-duplicates. Essays and study notes remain in their author-written language. The elaborate root homepage is kept at its established URL rather than duplicated prematurely.

Merge order / dependency

Merge PR #7 first, which adds the proper /zh/about/ canonical destination linked by this PR's navbar. PR #7 also corrects the academic CV from the owner's current two-page PDF. This branch starts cleanly from master and can be updated after #7 lands.

Acceptance

Review GitHub Actions build/audit for all ten paired research notes; test static English and Chinese index links, language button, direct /zh/research/... page access, and reciprocal hreflang. The newly added URLs should appear in sitemap when deployed.

Google source: https://developers.google.com/search/docs/advanced/crawling/managing-multi-regional-sites

Draft until those checks and a browser visual pass.

Homepage link behavior

The homepage retains its own familiar bilingual visual presentation at the stable root URL. On the Chinese setting, its eight research/project links (including the research index) now resolve to the matching Chinese URLs. The static English links remain readable to crawlers and no automatic language redirect is introduced.

The original About/CV profiles receive proper locale-specific URLs in PR #7 and should be merged before this PR.