chore(cleanup): replace hand-rolled i18n loader with i18next

[EtienneLescot]

Summary

Replaces the 126-line hand-rolled i18n loader in src/i18n/loader.ts with a ~70-line wrapper around the maintained i18next library. {{var}} interpolation, defaultNS, fallbackLng, and locale resource loading all come from the library; the public API (getAvailableLocales, getLocaleName, getLocaleShort, translate) and the existing call sites in I18nContext, LaunchWindow, and EditorTopBar are unchanged.

Heads-up: new runtime dependency

This PR adds i18next@^23.16.0 as a runtime dependency (it's the only new dep). The original audit marked this swap as "needs a maintainer's blessing" since it pulls a maintained library into the bundle. 23.x is the conservative pick (same major that was current when the audit was written); 26.x is the current stable and would also work for our minimal init + t surface.

Bundle cost: ~12 kB minified for i18next core (no plugins, no react-i18next, no backend — we feed the resources inline via import.meta.glob).

Maintainer eyeball pass

The library is wired to all 13 locales × 7 namespaces = 91 JSON files. The exists() + t() shim falls back to the en translation for missing keys at runtime (i18next handles this via fallbackLng: 'en'), and the existing src/i18n/__tests__/localeParity.test.ts already enforces that every locale has every en key at build time. A quick eyeball pass against the 91 files would be appreciated before merge.

Notes on interpolation behavior

The new loader uses i18next's default {{var}} regex, which matches the hand-rolled loader's /\{\{(\w+)\}\}/g exactly. The only intentional divergence: i18next is configured with interpolation: { escapeValue: false } because React escapes at the render boundary; the old loader had no escaping at all. This only matters if a translation value contains < or > — and since all of our vars are string | number (file names, project names, counts), the user-visible output is identical.

Test results

• npx tsc --noEmit: clean
• npx vitest --run src/i18n src/components/launch/LaunchWindow.test.tsx: 40/40 pass
• npx vitest --run src/: 904/904 pass; the only file-level failures are a pre-existing pixi.js resolution issue in this worktree's fresh install (unrelated to this change — same tests pass in the main checkout)
• npx biome check src/i18n/loader.ts package.json: clean

Diff summary

 package-lock.json | 375 +++++------------
 package.json       |   1 +
 src/i18n/loader.ts | 144 +++++++-----------
 3 files changed, 82 insertions(+), 438 deletions(-)

The package-lock.json diff is mostly stale-entry cleanup (28 packages like @langchain/langgraph, gsap, uuid, langsmith, emoji-picker-react, @pixi/filter-drop-shadow were no longer in package.json but still in the lock). One new entry: node_modules/i18next.

Type of change

• Refactor / maintenance

Release impact

• Minor

Desktop impact

• Not platform-specific

Testing

npx tsc --noEmit
npx vitest --run src/i18n src/components/launch/LaunchWindow.test.tsx
npx biome check src/i18n/loader.ts package.json

All clean. Full npm run test shows 904/904 pass; the few file-level failures are pre-existing pixi.js resolver issues in this worktree's fresh node_modules and are reproducible on the base branch with the worktree's node_modules state.

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