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>

tests/screen_text_en.h

@@ -3,12 +3,13 @@
 #pragma once
 #include "components/smart_display/screen_text.h"
 
-static_assert(screen_text::KEYS_HASH == 0xC6B1A3EDu && screen_text::KEY_COUNT == 305,
+static_assert(screen_text::KEYS_HASH == 0x5DBB4605u && screen_text::KEY_COUNT == 306,
               "screen_text_keys.h does not match screen_manager/translations/en.json: run tools/i18n.py header");
 const char *const screen_text::TABLE[] = {
     ".",
     ",",
     "1",
+    "%",
     "Just now",
     "{n} min ago",
     "1 hour ago | {n} hours ago",