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.

src/ui/styles/radio.css

@@ -49,7 +49,8 @@
 #radio-filter {
   /* Radio owns its compact density and arrow space; shared fields paint the
      palette and disabled state, including this intentional theme exception. */
-  padding: 7px 24px 7px 8px;
+  padding-block: 7px;
+  padding-inline: 8px 24px;
   border-radius: 5px;
   font: 9px/1.2 var(--font-mono);
   --gev-field-border-color: rgba(65, 220, 231, 0.28);
@@ -1128,7 +1129,8 @@ html:not([lang='en']) .data-row-list-text {
 .sdr-gain-row select {
   flex: 1;
   min-width: 0;
-  padding: 5px 22px 5px 7px;
+  padding-block: 5px;
+  padding-inline: 7px 22px;
 }
 .sdr-adsb-stats {
   display: grid;