Add /labs: the projects that are not released yet

[openipc-ai]

Part of #206 (Phase 1). Depends on nothing.

Why

June decided the site should show what the project is working on before it ships, and named four: free-drm, latency-meter, the NPU work on faces and licence plates, and the zynq7010 board. The component for it already exists: app/assets/stylesheets/components/_cards.scss is commented "Pillar cards (homepage) and project cards (ecosystem/labs)", and /ecosystem uses the project card today. Nothing else was built.

What to change

• pages#labs, /labs, full-bleed, one project card per project: name, one paragraph on what it is and why it matters to camera owners, a status line (idea, prototype, on a bench, code public), and a link to the repository if there is one or the words "not public yet" if there is not.
• English only at launch, as June decided. The i18n gate in test/controllers/relaunch_pages_test.rb is told the page is English-only so it does not fail on ru and zh; the page renders its English copy under every prefix rather than "translation missing".
• Ecosystem dropdown entry and sitemap entry. The homepage does not link it.
• The four status lines are checked against the repositories on the day the page lands, and the page shows the date it was last updated, so a stale status reads as stale rather than as a claim.

Done means

• /labs, /ru/labs, /zh/labs render the English page with no missing-translation string.
• Each card's status and link were verified against the project on the day of landing, and the check is described in the PR.
• Screenshots before any PR.