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]>

src/i18n/locales/es.json

@@ -1096,7 +1096,7 @@
   "FIELD REPORTS · {count}": "INFORMES DE CAMPO · {count}",
   "GEOLOCATIONS · {credit}": "GEOLOCALIZACIONES · {credit}",
   "↗ OPEN PUBLIC MAP": "↗ ABRIR MAPA PÚBLICO",
-  "Clouds are preserved from the source imagery.": "Las nubes provienen de las imágenes de origen.",
+  " Clouds are preserved from the source imagery.": " Las nubes provienen de las imágenes de origen.",
   "Show the Nepal context callout without a border or country fill": "Muestra la etiqueta de contexto de Nepal sin frontera ni relleno del país",
   "Introduce Nepal, draw its border, then reveal the Bhote Koshi incident": "Presenta Nepal, dibuja su frontera y luego revela el incidente del Bhote Koshi",
   "CITIES": "CIUDADES",
@@ -2890,5 +2890,9 @@
   "USB work abandoned after a stalled transfer": "Trabajo USB cancelado tras una transferencia bloqueada",
   "SDR decoder did not start; receiver stopped": "El decodificador SDR no arrancó; receptor detenido",
   "SDR decoder stopped responding; receiver stopped": "El decodificador SDR dejó de responder; receptor detenido",
-  "SDR decoder fell behind; receiver stopped": "El decodificador SDR se quedó atrás; receptor detenido"
+  "SDR decoder fell behind; receiver stopped": "El decodificador SDR se quedó atrás; receptor detenido",
+  "hemisphere|N": "N",
+  "hemisphere|S": "S",
+  "hemisphere|E": "E",
+  "hemisphere|W": "O"
 }