fix(source): localize Source labels and parsing via string resources

Replace Source enum string formatting/parsing logic with resource ID mapping so source labels are fully localized and no longer depend on hardcoded English values.

Move string resolution to UI call sites, update category-to-list navigation to pass @StringRes IDs, and add system_app translations for English, French, German, Spanish, and Italian.

Also update SourceTest to validate resource-based toString/fromString behavior.