Notation like Home Assistant, each screen in its own language, and the language in every build

From the end-to-end test on the bench boards and an independent review:
- Units spaced as Home Assistant does (54% / 54 % in German and French, 18°, 21.5 °C), in the firmware and the app.
- Grouping from five digits where the language does (1234 but 12.345 in Spanish, Polish, Portuguese): the layout
  message carries group_min and percent_space; an unknown number style no longer refuses a layout.
- Automatic follows Home Assistant's own language for the clock and numbers, also without a translation (Swedish:
  24 hours, 1 234,5; pt-BR: 1.234,5): regions.json from the CLDR for all 63 languages Home Assistant offers.
- 12-hour clock: the top bar says 3:48 PM, the clock card 3:48 (not 03:48), Last runs follow the clock.
- The climate setpoint font has the decimal comma; the value fonts have ², ³ and µ (m³ was a box).
- Weather days: at most three letters without the dot (mié, sáb, czw); the screen took three bytes.
- Texts fall back per key through the base language (pt-BR -> pt -> en) in the firmware and the app.
- Each screen gets the app's words in the language its firmware speaks; firmware from before the languages gets
  English and its own letters, not boxes.
- set_language re-reads what it writes (indentation, comments, quoted keys, CRLF, !include) and every build writes
  the language first; the 24-hour pin no longer hits a fresh install and waits for the old clock switches.
- Tests: region and notation, plural parity with the C++ rules, set_language edge cases, the pin, PUT /api/language.

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

components/smart_display/history_view.h

@@ -65,8 +65,7 @@ inline std::string duration(uint32_t seconds) {
 }
 
 // A value as Home Assistant writes it: fixed decimals, the language's separator between thousands and its decimal
-// mark (screen.number: "1,234.5" in English, "1.234,5" in Dutch), "%" and "°" on the number and any other unit after
-// a space.
+// mark (screen.number: "1,234.5" in English, "1.234,5" in Dutch), the unit spaced as Home Assistant spaces it.
 inline std::string number(float value, int decimals, const std::string &unit) {
   if (!std::isfinite(value)) return "--";
   char b[40];
@@ -77,9 +76,7 @@ inline std::string number(float value, int decimals, const std::string &unit) {
   std::string whole = text.substr(0, dot), rest = dot == std::string::npos ? "" : text.substr(dot);
   bool zero = whole.find_first_not_of('0') == std::string::npos && rest.find_first_not_of(".0") == std::string::npos;
   text = (zero ? "" : sign) + screen_text::write_number(whole, rest.empty() ? std::string() : rest.substr(1));
-  if (unit.empty()) return text;
-  if (unit == "%" || unit == "°") return text + unit;
-  return text + " " + unit;
+  return screen_text::with_unit(text, unit);
 }
 
 // Where part `i` of 24 is drawn and read: the middle of its stretch of the range, as a fraction of the width.