fix(outreach): translate docs sidebar section labels into French

[Shaji-Mohammed]

Fixes #1793.

What changed

The French docs sidebar showed English group headings. Starlight sidebar entries now carry translations: { fr: … }:

• Tutorials → Tutoriels, Reference → Référence, Changelog → Journal des modifications (astro.config.ts)
• Runtime Core API → API de Runtime Core, via a new optional translations field on the typedoc plugin's sidebar options

Introduction, Guides and Concepts are the same words in French. Pages in these sections stay English-only, per docs/AGENTS.md.

Why not the suggested fix

The issue suggests passing translations through getSidebarGroupFromPackageReflections / getSidebarGroupFromReflections. Both functions call themselves recursively with the same options object to build nested groups under their own labels (child.name). Reading options.translations there would give nested groups the top-level French label unless each call site added a condition. Instead, the translations are attached once in getSidebarFromReflections, where the top-level group replaces the sidebar placeholder. That function already applies badge there.

Verification

• pnpm lint green; outreach astro check 0 errors, build succeeds.
• Rebuilt outreach and compared all 300 built pages against the previous build. English pages are unchanged. On French pages the only differences are the translated labels and Starlight's sidebar-state hash. Nested typedoc groups keep their own names.
• pnpm test:coverage green (384/384 files, 100%), run with NODE_OPTIONS=--no-experimental-webstorage because the local machine is on Node 25.

Exceptions:

• No unit or e2e test: apps/outreach has no test suite, by decision (apps/outreach/AGENTS.md). The build comparison above is the check.
• pnpm test:e2e not run locally (Playwright browsers not installed). The e2e suite doesn't cover the outreach site, so CI's run covers it.