feat(portal-shell): i18n string sweep — mark UI strings + FR translations (#93)

## Summary

Continue ADR-0019 implementation. Mark every UI string surfaced by the shell with `i18n="@@id"` (templates) or `$localize` (TypeScript), and populate [`messages.fr.xlf`](apps/portal-shell/src/locale/messages.fr.xlf) with French translations. The production build now ships **two genuinely different bundles** under `dist/.../{en,fr}/`.

**43 trans-units** marked, grouped by feature:

| Surface | Strings |
|---|---|
| `app.html` | skip-link |
| `header.html` | wordmark, search label + placeholder, action button aria-labels, user-menu placeholder |
| `sidebar.ts` + `.html` | menu groups + items, aside / nav aria-labels, role badge, toggle button (Expand / Collapse aria + Collapse text) |
| `theme-switcher.ts` + `.html` | mode labels, menu aria, trigger aria (`Theme: <mode> (open menu)` with named placeholder) |
| `footer.html` | aria-labels, copyright (interpolation preserved) |
| `home.html` | welcome heading + intro + status widget labels |
| `app.routes.ts` | browser tab titles |

## Tooling

- Add `"@angular/localize"` to the `types` array in both [`tsconfig.app.json`](apps/portal-shell/tsconfig.app.json) and [`tsconfig.spec.json`](apps/portal-shell/tsconfig.spec.json) so TypeScript resolves the `$localize` global at compile time. Specs need it too — they evaluate the same component code paths.
- Extraction target (`nx run portal-shell:extract-i18n`) reports **44 messages** (43 unique IDs).

## Translation choices worth flagging

- **Wordmark**: "APF Portal" → "Portail APF". Same key used for the `/` browser tab title. The PWA manifest (`site.webmanifest`) stays "APF Portal" — manifest values are not bundled, they sit in the static assets and are language-neutral in v1.
- **System theme mode** → "Système".
- **"Anonymous"** role → "Anonyme"; **"Role:"** → **"Rôle :"** (French uses a non-breaking space before the colon — typographic convention, preserved in the XLIFF target).
- **Accessibility links in the footer stay bilingual.** Each carries its own `lang` attribute (`lang="en"` and `lang="fr"`). The dual-link pattern goes away in the upcoming route-fusion PR; until then it's the most honest stopgap.
- **Both accessibility routes share one title key** (`@@route.accessibility.title`). In the EN bundle, both display "Accessibility statement · APF Portal"; in the FR bundle, both display "Déclaration d'accessibilité · Portail APF". After route fusion only one route remains.

## Verification

- Production build: **129 kB gzip initial per locale** (vs 122 kB before). +7 kB absorbs the i18n marker metadata and the embedded translation data in the FR bundle. Well under the 300 KB budget.
- Spot-checked the FR bundle: no leftover English source text on any swept string, route title, or home page intro. The `Welcome to APF Portal` in the lazy `home` chunk shows "Bienvenue sur Portail APF" in FR.
- **36 / 36 specs unchanged.** They run in the source locale (`en`), so the English assertions still match. No spec edits needed.
- Lint clean.

## Out of scope (each its own follow-up PR)

- **Locale switcher in the footer** + `__Host-portal_locale` cookie + smart `/` redirect.
- **Collapse `/accessibility` + `/accessibilite`** into one localised route with locale-translated path segments.
- **CI gate** that fails the build on a missing translation. Once the sweep is reviewed, we add `nx build --localize` to `ci:check` and verify it rejects unsealed strings.
- **Accessibility page content localisation.** Its content is driven by a `copy()` service rather than i18n-marked templates — restructured during the route fusion.

## Test plan

- [x] `pnpm exec nx run-many -t lint test build --projects=portal-shell` — green (36 / 36 specs).
- [x] `pnpm exec nx run portal-shell:extract-i18n` — clean, 43 unique unit IDs.
- [x] Production build emits both locales; FR bundle contains "Tableau de bord", "Aller au contenu principal", etc.
- [ ] Manual: `pnpm exec nx serve portal-shell` shows the EN source. `pnpm exec nx build portal-shell --configuration=production && pnpm exec nx run portal-shell:serve-static` → open `http://localhost:4200/fr/` for FR, `/en/` for EN.
- [ ] Manual: every aria-label announced by a screen reader in FR build matches the French translation.
- [ ] Manual: browser tab title flips between bundles ("APF Portal" vs "Portail APF").

---------

Co-authored-by: Julien Gautier <julien.gautier@apf.asso.fr>
Reviewed-on: #93

apps/portal-shell/src/app/app.routes.ts

@@ -1,11 +1,18 @@
 import { Route } from '@angular/router';
 
+// Tab titles per route — marked with `$localize` so each locale's
+// bundle ships its own. The `/accessibility` and `/accessibilite`
+// pair shares a title key; the upcoming route fusion (per ADR-0019)
+// collapses them to a single localised route.
+const homeTitle = $localize`:@@route.home.title:APF Portal`;
+const accessibilityTitle = $localize`:@@route.accessibility.title:Accessibility statement · APF Portal`;
+
 export const appRoutes: Route[] = [
   {
     path: '',
     pathMatch: 'full',
     loadComponent: () => import('./pages/home/home').then((m) => m.Home),
-    title: 'APF Portal',
+    title: homeTitle,
   },
   // RGAA + ADR-0016: the accessibility statement must be reachable
   // from both locales' canonical paths. Same component, content
@@ -15,13 +22,13 @@ export const appRoutes: Route[] = [
     loadComponent: () =>
       import('./pages/accessibility/accessibility').then((m) => m.AccessibilityStatement),
     data: { lang: 'en' },
-    title: 'Accessibility statement · APF Portal',
+    title: accessibilityTitle,
   },
   {
     path: 'accessibilite',
     loadComponent: () =>
       import('./pages/accessibility/accessibility').then((m) => m.AccessibilityStatement),
     data: { lang: 'fr' },
-    title: 'Déclaration d’accessibilité · APF Portal',
+    title: accessibilityTitle,
   },
 ];