Refactor stalker-series-view template to guard fields with conditionals
so that only available metadata is displayed. Replace selectedItem() with
displayItem() to use the updated selection accessor. Add checks for
director, actors, year/release date, genre/genres_str, imdb and kinopoisk
ratings to avoid showing empty labels.
Enhance stalker-portal-import component by adding reactive form fields
for serial/device IDs and signatures, importing MatProgressSpinnerModule,
and wiring TranslateService and StalkerSessionService into the component.
Include a small loading-container style. These changes prepare the UI for
improved import UX and safer rendering of optional series metadata.
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