i18n(ar): mirror the layout right to left

- The title, style indicator and both rails swap sides in RTL through logical
  properties (inset-inline-*, margin-inline-*, border-inline-start); LTR
  computes the same values. The Display/Context rail keeps its physical
  `right` for the credit-clearance model and swaps in rtl.css above 720px.
- rtl.css: no letter-spacing on Arabic (it tears joined letters apart);
  Noto Sans Arabic leads the Arabic font stacks so words are not set in a
  fixed-pitch fallback; the intel HUD and cockpit instruments stay a
  left-to-right instrument overlay; media transport and the radio dial stay
  left to right; feed headlines and station names take their own direction;
  the moved rail's arrows flip.
- isolate(): a quantity in RTL text (2.7 كم, -18.0°) is wrapped in
  first-strong isolates so its digits do not join a neighbouring Latin run.

Co-Authored-By: Claude Opus 5.5 <[email protected]>

src/ui/unitLabels.js

@@ -1,4 +1,4 @@
-import { formatNumber, msg, t } from '../i18n/index.js';
+import { formatNumber, isolate, msg, t } from '../i18n/index.js';
 
 // Unit ids stay English in data, params and AI-tool readings; only the label
 // shown on the page is translated. dBZ and °C read the same in every language.
@@ -30,7 +30,7 @@ export function unitLabel(unit) {
 export function formatQuantity(value, unit, options) {
   const label = unitLabel(unit);
   const number = formatNumber(value, { useGrouping: false, ...options });
-  return label ? `${number}\u00a0${label}` : number;
+  return label ? isolate(`${number}\u00a0${label}`) : number;
 }
 
 /**