Modernize site: self-contained Hugo setup, new design, current CI

[emptymalei]

Why

The site no longer built on current Hugo: the theme used APIs removed years ago, and CI was pinned to Hugo 0.68.3. This rebuilds it on a current toolchain and refreshes the design. All existing page URLs are preserved.

What changed

• Self-contained. The themes/interimm submodule is vendored into this repo (layouts, data, i18n, assets at the site root). The shared theme repo InterImm/hugo-interimm-template is not modified.
• Much lighter. Bulma, bulmaswatch, Font Awesome, Algolia InstantSearch and several small CSS libs are replaced by one hand-written, fingerprinted stylesheet and about 40 lines of JS. Render-critical CSS/JS/HTML goes from about 620 KB to about 8 KB gzipped; no third-party requests on normal pages.
• Design and accessibility. Automatic light/dark mode, responsive layout, skip link, keyboard-accessible dropdowns, labelled controls, reduced-motion support. Palette checked against WCAG AA.
• SEO and metadata. Valid lang (zh-CN/en), hreflang, canonical and OG tags with an absolute baseURL, JSON-LD, sitemap in robots.txt. Section pages (archives, cities, institutes) are no longer noindex.
• City map. Now an imagemap shortcode (Leaflet 1.9.4 with SRI) driven by front matter. The English city page was stale (old hub links, 3 of 4 markers) and now shares the current data.
• Data and content. Emoji icons replace icon-font classes; http:// links to hosts that serve HTTPS are upgraded; the English "Welcome on Board" button now goes to /archives/ instead of the empty /guide page; a duplicate Discord link in the English footer is removed.
• CI and deploy. Hugo 0.135.0 with current actions on ubuntu-latest. Deployment moves to GitHub Pages' official upload-pages-artifact + deploy-pages flow (no more generated master branch). Pull requests only verify the build; pushes to hugo publish; the workflow can also be run manually.

Needs a decision or a look

• Required before the first deploy: switch the Pages source. Settings > Pages > Build and deployment > Source must change from "Deploy from a branch" (master) to GitHub Actions. Until then the deploy job fails and the current site stays live. Suggested order: merge, switch the setting, then re-run the workflow (or push). The custom domain interimm.org is stored in the Pages settings and carries over. Optionally enable "Enforce HTTPS" at the same time; it is currently off.
• Analytics is off. The old Universal Analytics property (UA-50146153-1) stopped collecting in 2023. To enable GA4, add a measurement ID under services.googleAnalytics.id in hugo.yaml (commented hook included).
• Deleted public files. Old /css/bulma*, /js/*, /assets/{galleria,swiper,bulma-carousel,search}, /images/{icons,social,search}, and leftover "KasualFlow" template logos under /images/logos and /uploads. Nothing in this repo references them, and the sibling projects I checked (hub, mars-map, mars-clock, comms-latency, solarsystem) don't either. Public icon, map and media paths are unchanged.
• Removed URLs. Only empty RSS feeds, empty categories/keywords pages and the /cities/page/1/ pagination stub.
• Left alone on purpose. /guide is still an empty page; two http:// links (exponentialdeepspace.org, computational-communication.com) stay because those hosts don't answer over HTTPS; the large .psd/.xcf design sources are still served from /images/about/; the English city page text is still Chinese.

Testing

• hugo --minify --gc builds with no warnings on Hugo 0.135.0. The URL inventory was compared against a patched build of the old site.
• All local links and assets in the built output resolve; sibling-project links on interimm.org return 200.
• Checked in a browser: desktop and mobile, light and dark, Chinese and English, dropdown/Escape behaviour, mobile menu, map popups, 404 page.
• Not tested: an actual deploy, other Hugo versions, non-Chromium browsers. The CI check on this PR will confirm the build on the pinned version.

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