i18n(ar): own the Arabic catalog in the application package; mirror select chevrons

The application package boundary owns src/i18n/locales/ar.json beside the
other catalogs, and the style.css shim test checks that the shim holds only
import statements rather than counting its lines, so adding rtl.css to it
does not read as rules.

Selects pad the chevron's side with padding-inline-end, as do the Radio
filter, the SDR gain select and the voice timeout select, which set their
own padding; rtl.css moves the chevron to the left, where an Arabic field's
text ends. A rail legend's range keeps left-to-right order under its colour
ramp, which always runs low to high from left to right.

scripts/package-boundaries.json

@@ -60,6 +60,7 @@
       "src/ui/scenePresentation.js",
       "src/i18n/index.js",
       "src/i18n/locale.js",
+      "src/i18n/locales/ar.json",
       "src/i18n/locales/de.json",
       "src/i18n/locales/es.json",
       "src/i18n/locales/fr.json",