i18n(ja): address code review findings

Japanese has no letter case, so the HUD summary keeps units as the
catalog writes them (13 km), matching the cockpit and the ja HUD CSS.
The ja '{value} KM', '{value} KM/H' and '{value} KM/S' strings are now
lower-case like zh-CN.

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

src/i18n/locales/ja.json

@@ -803,8 +803,8 @@
   "DATE UNAVAILABLE": "日付不明",
   "UNSPECIFIED OPERATOR": "運用者未指定",
   "Select {mission}": "{mission}を選択",
-  "{value} KM": "{value} KM",
-  "{value} KM/S": "{value} KM/S",
+  "{value} KM": "{value} km",
+  "{value} KM/S": "{value} km/s",
   "Selected Space Mission": "選択中の宇宙ミッション",
   "SELECTED SPACE MISSION": "選択中の宇宙ミッション",
   "Show all missions": "すべてのミッションを表示",
@@ -1607,7 +1607,7 @@
   "REGION UNAVAILABLE": "地域を取得できません",
   "NO RECENT LOCATION MATCHES": "この地域の最近のニュースなし",
   "{domain} · {age}": "{domain} · {age}",
-  "{value} KM/H": "{value} KM/H",
+  "{value} KM/H": "{value} km/h",
   "CLOUD {pct}%": "雲量 {pct}%",
   "CLOUD UNKNOWN": "雲量不明",
   "{source} · LOCATION QUERY": "{source} · 位置クエリ",