i18n(zh-CN): complete and ship Simplified Chinese

- Translate the remaining 910 strings and review the whole catalog (meaning,
  terms, punctuation, label length) against the screens.
- Register zh-CN: any zh tag maps to it except Traditional ones (Hant, TW,
  HK, MO), which keep English until a Traditional catalog ships.
- Hemisphere letters get their own context so the HUD sector line reads
  21.33N, not a compass word; the Bhote Koshi imagery dates follow
  year-first languages (2021年10月16日).
- cjk.css: tight tracking for Chinese text and a 9px floor on the dock voice
  labels and layer buttons; Latin HUD readouts keep their look.
- docs/translations/zh-CN.md: style, plurals and glossary.

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

docs/CURRENT-STATE.md

@@ -3369,7 +3369,7 @@ test:track` 43 tracking invariants · headless QA harnesses under
 
 ### Interface localization (October 2026)
 
-Shipped locales: **en** (source and fallback), **es** and **ru**. The code lives in
+Shipped locales: **en** (source and fallback), **es**, **ru** and **zh-CN**. The code lives in
 `src/i18n/`. How to mark UI text: [`docs/I18N.md`](./I18N.md); translator workflow:
 [`docs/TRANSLATORS.md`](./TRANSLATORS.md).
 
@@ -3380,7 +3380,9 @@ Shipped locales: **en** (source and fallback), **es** and **ru**. The code lives
   value). English has no catalog; every other locale is
   `src/i18n/locales/<code>.json`, and a missing entry falls back to English.
 - **Locale choice.** `?lang=` → stored choice (`gev:locale:v1`) →
-  `navigator.languages` → English. `?lang=` is not stored, and share links drop
+  `navigator.languages` → English. Any `zh` tag maps to `zh-CN` except
+  Traditional ones (`Hant`, `TW`, `HK`, `MO`), which fall through until a
+  Traditional catalog ships. `?lang=` is not stored, and share links drop
   it, so a recipient keeps their own language. The globe picker in the
   bottom-right corner (`src/ui/localePicker.js`) stores the choice, drops
   `?lang=` (keeps it only when storage is blocked) and reloads. It asks first

docs/TRANSLATORS.md

@@ -1,6 +1,6 @@
 # Translating God's Eye View
 
-Shipped languages: **English** (source and fallback), **Spanish** (`es`) and **Russian** (`ru`).
+Shipped languages: **English** (source and fallback), **Spanish** (`es`), **Russian** (`ru`) and **Simplified Chinese** (`zh-CN`).
 
 ## How it works
 
@@ -63,4 +63,4 @@ These are contracts, not copy: layer ids and registry keys, status enums and oth
 
 ## Language notes
 
-Each language keeps its glossary, plural forms, units and style in its own file, `docs/translations/<code>.md`: [Spanish](./translations/es.md), [Russian](./translations/ru.md). Read it before translating, and add a term there when you settle on one.
+Each language keeps its glossary, plural forms, units and style in its own file, `docs/translations/<code>.md`: [Spanish](./translations/es.md), [Russian](./translations/ru.md), [Simplified Chinese](./translations/zh-CN.md). Read it before translating, and add a term there when you settle on one.

docs/translations/zh-CN.md

@@ -0,0 +1,59 @@
+# Simplified Chinese (`zh-CN`)
+
+Catalog: `src/i18n/locales/zh-CN.json`. General rules: [TRANSLATORS.md](../TRANSLATORS.md).
+
+The catalog started from the Chinese locale by abiyeenzo (#914) and the
+Simplified Chinese localization by EDIT-Aeterna (#979); the rest was translated
+for the current English and reviewed against both.
+
+## Style
+
+- Mainland usage and Simplified characters. Address the user neutrally, without 您/你 where a plain imperative works: 「点击地图」, 「重试」.
+- Chinese has no case: an UPPERCASE English HUD label becomes the same short Chinese label. Keep labels as short as the English: 「实时」, 「过期」, 「关」.
+- Full-width punctuation in Chinese text: ，。：；？！（）“”. A dash is 「——」 without spaces; keep `·` as the HUD separator and `…` for ellipsis.
+- One space between Chinese and Latin letters or digits: 「AIS 船舶」, 「24 小时」, 「{count} 个」. No space next to full-width punctuation.
+- Units: km, m, km/h, m/s, kn, ft, MW, °, % stay as written; time words are 小时, 分钟, 秒 after a number (「5 分钟前」).
+- Product names, provider names and codes stay as they are: Google, Cesium, CelesTrak, NOAA, FIRMS, AIS, ADS-B, GNSS, CCTV, HUD, CRT, NVG, FLIR, WHOT/BHOT, Ironbow, CONUS.
+
+## Plurals
+
+`Intl.PluralRules('zh-CN')` has one category, `other`: a `tn()` entry has only that form. Use a measure word next to the number where Chinese needs one: 「{count} 个密钥」, 「{count} 架飞机」, 「{count} 艘船」.
+
+## Glossary
+
+| English                               | 中文                        |
+| ------------------------------------- | --------------------------- |
+| layer / data layer                    | 图层 / 数据图层             |
+| feed                                  | 数据源                      |
+| source / data source                  | 来源 / 数据源               |
+| LIVE (status) / live data             | 实时 / 实时数据             |
+| SIMULATED                             | 模拟                        |
+| stale / degraded / unavailable        | 过期 / 降级 / 不可用        |
+| retry                                 | 重试                        |
+| key (API key) / POWER UP              | 密钥（API 密钥）/ 增强      |
+| Provider Settings                     | 服务商设置                  |
+| globe / map / map source / basemap    | 地球 / 地图 / 地图源 / 底图 |
+| aircraft / flight / military flights  | 飞机 / 航班 / 军用航班      |
+| vessel, ship                          | 船舶                        |
+| satellite                             | 卫星                        |
+| launch (rocket) / space mission       | 发射 / 太空任务             |
+| contact (tracked object)              | 目标                        |
+| installation, site                    | 设施                        |
+| camera / CCTV camera                  | 摄像头 / CCTV 摄像头        |
+| earthquake / active fire              | 地震 / 活跃火点             |
+| scene / shot                          | 场景 / 镜头                 |
+| briefing / panel / dock               | 简报 / 面板 / 停靠栏        |
+| preset / visual preset                | 预设 / 视觉预设             |
+| Display / HUD layout                  | 显示 / HUD 布局             |
+| Tactical / Operator / Minimal / Cyber | 战术 / 操作员 / 精简 / 赛博 |
+| Scope (circular viewport mask)        | 视域                        |
+| Clean UI                              | 纯净界面                    |
+| cockpit                               | 座舱                        |
+| heading / altitude / ground speed     | 航向 / 高度 / 地速          |
+| Street Level / Street View (Google)   | 街景 / 街景（Google）       |
+| Recent Imagery                        | 近期影像                    |
+| Global Context / Context (panel)      | 全局态势 / 态势             |
+| radio (station)                       | 电台                        |
+| transit / bikeshare                   | 公共交通 / 共享单车         |
+| Previous / Next                       | 上一个 / 下一个             |
+| compass points (N, NNE, …)            | 北, 北东北, …               |