Switch language in place, without a reload

Choosing a language in the picker now applies it at once. The choice is
stored and ?lang is kept in step through replaceState, and the picker keeps
focus.

Code that writes translated text itself re-presents it on a switch:
onLocaleChange() lets an owner listen, removed at teardown, and status
writers hand over a function of the locale (voice cards, scene director,
SDR, draw hints, imagery split, map sources, Bhote Koshi media) so the
words are rebuilt rather than re-sent. The HUD, cockpit, radio, CCTV,
launch, awareness and credit texts follow the same hook, and
applyDocumentTranslations can be applied again without undoing text code
wrote since.

The unsaved-work registry and persistLocaleAndReload existed only to guard
the reload, so they go, with their catalog entries.

src/i18n/locales/zh-Hant.json

@@ -9,7 +9,6 @@
   "That line has no length — click somewhere further away.": "這條線沒有長度——請在更遠處點擊。",
   " · {max}-point limit reached": " · 已達 {max} 個點上限",
   "{measure} · double-click or Enter to finish, Backspace undoes, Esc cancels.{full}": "{measure} · 雙擊或按 Enter 完成，按 Backspace 撤銷，按 Esc 取消。{full}",
-  "drawings on the map": "地圖上的繪圖",
   "That shape already has {count} points — finish it or press Backspace.": "該形狀已有 {count} 個點——請完成繪製或按 Backspace。",
   "That point is off the globe — click on the world.": "該點在地球之外——請點擊地球上的位置。",
   "That shape could not be placed.": "該形狀無法放置。",
@@ -394,7 +393,6 @@
   "paste {envVar}": "粘貼 {envVar}",
   "REMOVE": "移除",
   "Remove {title} from this app's saved keys": "從本應用已保存的密鑰中移除 {title}",
-  "unsaved provider keys": "未保存的服務商密鑰",
   "Project keys: {status}": "項目密鑰：{status}",
   "your app configuration": "你的應用配置",
   "your local .env": "你的本地 .env",
@@ -1465,9 +1463,6 @@
   "Sensitivity": "靈敏度",
   "WHOT/BHOT": "WHOT/BHOT",
   "Ironbow": "Ironbow",
-  "unsaved CCTV calibration": "未保存的 CCTV 校準",
-  "the open cockpit": "當前打開的座艙",
-  "Switching language reloads the page. This will be lost: {items}. Switch anyway?": "切換語言會重新加載頁面。以下內容將會丟失：{items}。仍要切換嗎？",
   "VISUAL PRESETS": "視覺預設",
   "LOCATION": "位置",
   "CONTACTS — nearest planes · vessels · sites": "目標：最近的飛機 · 船舶 · 設施",
@@ -1676,7 +1671,6 @@
   "Space Missions": "太空任務",
   "Context": "態勢",
   "Rendered globe frames per second · toggle with `": "每秒渲染的地球幀數 · 按 ` 鍵切換",
-  "imported map files": "已導入的地圖文件",
   "Ground heights could not be refreshed. Try the file again when the map has loaded.": "無法刷新地面高度。請在地圖加載完成後重新嘗試該文件。",
   "{count} map objects": {
     "other": "{count} 個地圖對象"
@@ -2303,7 +2297,6 @@
   "Activate to toggle voice": "點擊切換語音",
   "Voice active": "語音已啟用",
   "Voice could not be started.": "無法啟動語音。",
-  "the active voice session": "當前語音會話",
   "{value} feet": "{value} 英尺",
   "The flights layer is not enabled": "航班圖層未開啟",
   "The military layer is not enabled": "軍用航班圖層未開啟",