feat(admin): localize the operator app with react-i18next (3/4)

[marcelo-maciel]

clients/admin slice of the i18n work, split out of #1344. 111 files, of which 30 are JSON catalogs. Mostly mechanical, as you predicted.

Independent of the backend slices. Nothing here needs the API change, and the API change needs nothing here. It can be reviewed and merged in any order relative to the other three.

Slice	Files	PR
Framework	56	#1360 — the hard review
Module catalogs and wiring	229	#1361 — depends on the framework slice
clients/admin	111	this one
clients/dashboard	134	#1363 — independent

What is in here

• react-i18next wiring in src/i18n.ts. The chosen language is persisted to the user profile and sent to the API as Accept-Language through apiFetch; variants are canonicalised onto a supported tag before the call, so the API never sees a bare pt.
• en-US and pt-BR catalogs, split per feature namespace, held at strict key and placeholder parity in both directions by tests/i18n/parity.spec.ts — a missing or mis-arged translation fails the build instead of shipping English.
• Language switcher in the topbar, and html[lang] follows the active language through a languageChanged listener. The app previously shipped a static lang="en" that nothing updated, so a Portuguese UI announced itself as English to screen readers and browser translation.
• Formatting stays in the presentation layer (src/lib/format.ts). That is the other half of the framework slice's UI-culture-only decision: the API pins CultureInfo.CurrentCulture to invariant and the app formats numbers, dates and currency itself.
• Impersonation handoff carries locale in the URL. StartImpersonation strips the target's locale claim on purpose, and the two apps normally sit on different origins, so there was no other way to convey it and the API fell through to the dashboard's own browser detection. Harmless on its own: on main nothing reads the parameter until the dashboard slice lands, and this PR's handoff-locale.spec.ts passes with only this half present.

Testing

Everything below is this slice on its own, at main plus these 111 files — not a share of the unsplit branch's totals.

• npm ci, npm run build (tsc -b + vite build), npx tsc -b tsconfig.tests.json and npm run lint: all exit 0.
• Playwright, full suite: 135 passed, 0 failed, 0 flaky, 0 skipped — the same count as on the unsplit branch, so nothing was lost in the cut. That includes tests/impersonation/handoff-locale.spec.ts, which passes with only this half of the handoff present.

src/Directory.Packages.props

One backend file in a React PR, which needs explaining. template-smoke.yml triggers on paths: clients/** and runs dotnet build on the scaffolded solution, and .template.config/template.json does not exclude src/Tests/** — so a front-end-only PR still restores the full package graph and hits NU1903 / GHSA-q939-rpr3-3284 on SSH.NET 2025.1.0, pulled transitively by Testcontainers. That advisory fails restore on main too, re-verified today at 3f2959e6.

The pin is byte-identical to #1333, which owns the fix, so both stay mergeable in either order and this copy can simply be dropped once #1333 lands. All four slices carry it for the same reason. Full rationale in the framework PR.

Notes

• The topbar's language hydration stops once the user chooses a language in-session, guarding against a stale profile save echoing the old locale back. That guard has no regression test: reproducing it needs an in-mount profile refetch driven through the Settings form, and the click races the language-change re-render (element detached from the DOM). Three distinct approaches, then stopped rather than paper over it with retries or a longer timeout. The underlying lost update on PUT /identity/profile is tracked in #1359, where the ponytail: comments in the topbar point.
• SignalR does not carry the app locale: the hub client builds its own requests instead of going through apiFetch, so Accept-Language on the negotiate is the browser's. Applies to every session, not just impersonation. Named explicitly in handoff-locale.spec.ts so any other channel that stops carrying the locale fails the test.

Docs (Golden Rule #10)

fullstackhero/docs#238, kept as a single PR covering all four slices — internationalization.mdx is one page whose sections map across the split. The Frontend (admin and dashboard) section is this slice and the dashboard one: catalogs, language detection and normalization, Accept-Language, the switcher and locale-aware formatting. That PR should merge after the last of the four, so the page never describes code that is not on main yet.

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