feat(roadtrip): give the corridor hits their own icons, and say when a stretch went unsearched

A petrol station and a campsite both came back as the same nameless grey dot, because
the road categories only existed on the server: the map falls back to grey for a
category it does not know. They now sit in the client's category table too — with the
pump, the bolt, the parking sign and the tent, in their own colours — which both map
renderers and the popup read from the same place.

They stay out of the explore pill's own list on purpose: that pill offers what a city
visit needs, and while road trip mode is on it is not on screen anyway.

The search also stayed quiet when only some boxes failed, which reads as "no fuel on
this stretch" when the truth is that nobody looked. A partial failure now says how many
stretches went unanswered.

shared/src/i18n/ar/roadtrip.ts

@@ -25,6 +25,7 @@ const roadtrip: TranslationStrings = {
   'roadtrip.poi.search': 'ابحث على طول المسار',
   'roadtrip.poi.searching': 'جارٍ البحث {done} من {total}',
   'roadtrip.poi.capped': 'المسار طويل — تم البحث في الجزء الأول فقط.',
+  'roadtrip.poi.partial': 'تعذّر البحث في {count} من المقاطع — لم يستجب البحث عن الأماكن.',
   'roadtrip.poi.failed': 'البحث عن الأماكن لا يستجيب حاليًا.',
   'roadtrip.poi.empty': 'اختر ما تحتاجه ثم ابحث.',
   'roadtrip.poi.add': 'إضافة',