Sun-based night dimming; separate marker for Heavy aircraft

Night dimming now uses the actual sunrise/sunset at the active
location (classic Almanac algorithm) instead of a fixed 22:00-06:00
window, with a fallback to that fixed window while location or time
isn't known yet. Applies to both the backlight (main.cpp) and the
radar's own color dimming (radar_screen.cpp).

Heavy-category aircraft (ADS-B emitter category "A5") now get a
distinct marker (larger circle with an outer ring, plus the usual
heading line) instead of sharing the orange "notable" ring, on both
the device display and the WebUI radar.

Note: the orange "notable" ring itself (military/government callsign
prefixes) remains unimplemented - Config::NOTABLE_CALLSIGN_PREFIXES
has never been defined anywhere in this project. The WebUI radar's
"notable" field is hardcoded false until that's actually specified;
on the device it was never wired up in the first place.

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

src/i18n_en.h

@@ -56,7 +56,7 @@ static const char* const I18N_EN[] = {
     "Manage WiFi networks",
     "Location presets",
     "Screen timeout: ",
-    "Night dimming (10pm-6am): ",
+    "Night dimming (sun-based): ",
     "Statistics",
     "History chart",
     "Logbook files",