fix(language-switcher): initialize currentLang$ after availableLanguages is resolved

[giulio-leone]

What

Closes #596 — Fixes both the logical and graphical problems with <it-language-switcher>.

Logical fix

The currentLang$ observable was created in the constructor, before availableLanguages was resolved in ngOnInit(). The startWith → map pipeline's first emission ran this.availableLanguages?.find(...) against undefined, always returning undefined and permanently showing the fallback text "Seleziona una lingua".

Fix: Move observable initialization into ngOnInit(), after availableLanguages is populated. The component now correctly shows the current language label (e.g. "ITA", "ENG") from the first render.

Graphical fix (positioning)

The dropdown positioning issue was a side effect: the longer fallback string caused the button to be wider than the final label, leading to a miscalculated dropdown position. With the correct label rendered from the first paint, the dropdown positions correctly.

How

- protected currentLang$: Observable<AvailableLanguage | undefined>;

- constructor() {
-   this.currentLang$ = this.translateService.onLangChange.pipe(...);
- }

  ngOnInit(): void {
    // ... availableLanguages resolution (unchanged) ...

+   this.currentLang$ = this.translateService.onLangChange.pipe(
+     startWith({ lang: this.translateService.getCurrentLang() }),
+     map(event => this.availableLanguages?.find(l => l.code === event.lang))
+   );
  }

Tests

• 115/115 tests pass (0 lint errors)
• 7 new tests covering:
  • Default language shown on init (ITA, ENG)
  • availableLanguages auto-resolved from TranslateService
  • Custom availableLanguages input + TranslateService registration
  • Language switching updates displayed label
  • Dropdown items rendered correctly

Migration

None — fully backward compatible.

⚠️ This reopens #630 which was accidentally closed due to fork deletion.