Build each screen in one language: the screen texts from the translations, European letters in the fonts, and Language & region in the app

The firmware takes its texts from screen_manager/translations/<code>.json at build time (components/smart_display:
one table in main.cpp, keys in screen_text_keys.h), and the fonts carry every letter European languages write with.
The app keeps Settings -> Language & region (language, clock, numbers) for every screen, writes LANGUAGE into the
screens' YAML and sends the clock and the number format in the layout message; the per-screen 24-hour clock goes.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

screen_manager/translations/en-GB.json

@@ -0,0 +1,16 @@
+{
+  "_meta": {
+    "name": "English (UK)",
+    "english": "English (UK)",
+    "script": "latin",
+    "plural": "one_other",
+    "clock": "24",
+    "checked": true
+  },
+  "screen": {
+    "light": {
+      "color": "Colour",
+      "color_temperature": "Colour temperature"
+    }
+  }
+}