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-CN.json

@@ -9,7 +9,6 @@
   "That line has no length — click somewhere further away.": "这条线没有长度——请在更远处点击。",
   " · {max}-point limit reached": " · 已达 {max} 个点上限",
   "{measure} · double-click or Enter to finish, Backspace undoes, Esc cancels.{full}": "{measure} · 双击或按 Enter 完成，按 Backspace 撤销，按 Esc 取消。{full}",
-  "drawings on the map": "地图上的绘图",
   "That shape already has {count} points — finish it or press Backspace.": "该形状已有 {count} 个点——请完成绘制或按 Backspace。",
   "That point is off the globe — click on the world.": "该点在地球之外——请点击地球上的位置。",
   "That shape could not be placed.": "该形状无法放置。",
@@ -394,7 +393,6 @@
   "paste {envVar}": "粘贴 {envVar}",
   "REMOVE": "移除",
   "Remove {title} from this app's saved keys": "从本应用已保存的密钥中移除 {title}",
-  "unsaved provider keys": "未保存的服务商密钥",
   "Project keys: {status}": "项目密钥：{status}",
   "your app configuration": "你的应用配置",
   "your local .env": "你的本地 .env",
@@ -1470,9 +1468,6 @@
   "Sensitivity": "灵敏度",
   "WHOT/BHOT": "WHOT/BHOT",
   "Ironbow": "Ironbow",
-  "unsaved CCTV calibration": "未保存的 CCTV 校准",
-  "the open cockpit": "当前打开的座舱",
-  "Switching language reloads the page. This will be lost: {items}. Switch anyway?": "切换语言会重新加载页面。以下内容将会丢失：{items}。仍要切换吗？",
   "VISUAL PRESETS": "视觉预设",
   "LOCATION": "位置",
   "CONTACTS — nearest planes · vessels · sites": "目标：最近的飞机 · 船舶 · 设施",
@@ -1686,7 +1681,6 @@
   "Space Missions": "太空任务",
   "Context": "态势",
   "Rendered globe frames per second · toggle with `": "每秒渲染的地球帧数 · 按 ` 键切换",
-  "imported map files": "已导入的地图文件",
   "Ground heights could not be refreshed. Try the file again when the map has loaded.": "无法刷新地面高度。请在地图加载完成后重新尝试该文件。",
   "{count} map objects": {
     "other": "{count} 个地图对象"
@@ -2315,7 +2309,6 @@
   "Activate to toggle voice": "点击切换语音",
   "Voice active": "语音已启用",
   "Voice could not be started.": "无法启动语音。",
-  "the active voice session": "当前语音会话",
   "{value} feet": "{value} 英尺",
   "The flights layer is not enabled": "航班图层未开启",
   "The military layer is not enabled": "军用航班图层未开启",