feat(i18n): add full Arabic (ar) translation

Adds a complete Arabic locale (2759 keys, full parity with en) and wires
it into routing, RTL direction detection, message loading, the language
switcher, and flag icons alongside the existing he/fa RTL locales.

components/ui/flag-icons.tsx

@@ -274,6 +274,18 @@ const skCross =
   " 7.22 49.54 7.11-.62-20.5-6.6-46.33-6.6-46.33s12.3.96 17.22.96c4.92 0" +
   " 17.21-.96 17.21-.96s-5.97 25.83-6.6 46.33c12.18.1 29.72-.49 49.55-7.11" +
   " 0 0-.62 8.3-.62 17.98 0 9.67.62 17.98.62 17.98-19.86-6.64-37.42-7.22-49.6-7.12v32.37";
+/** Arabic – Pan-Arab colours (black/white/green horizontal, red hoist triangle) */
+export function FlagArab(props: FlagProps) {
+  return (
+    <svg xmlns="http://www.w3.org/2000/svg" viewBox="0 0 6 4" width={W} height={H} className={flagClass} {...props}>
+      <rect width="6" height="4" fill="#fff" />
+      <rect width="6" height="1.33" fill="#000" />
+      <rect y="2.67" width="6" height="1.33" fill="#007A3D" />
+      <polygon points="0,0 2.4,2 0,4" fill="#CE1126" />
+    </svg>
+  );
+}
+
 const skHills =
   "M270 329.1c-24.87 0-38.19 34.46-38.19 34.46s-7.4-16.34-27.68-16.34" +
   "c-13.73 0-23.82 12.2-30.25 23.5 24.97 39.7 64.8 64.2 96.11 79.28" +
@@ -319,4 +331,5 @@ export const flagComponents: Record<string, (props: FlagProps) => ReactElement>
   zh: FlagCN,
   fa: FlagIR,
   he: FlagIL,
+  ar: FlagArab,
 };