Scrolling marquee for radar info line, clearer tap hint text

The bottom info line on the radar screen (tap hint / empty-sky timer)
is now a continuously scrolling marquee instead of static text,
consistent with the nearest-airport ticker on the Location Presets
screen. The text is redrawn every tick() call (80ms) rather than only
on render(), so it scrolls smoothly and the empty-sky second counter
keeps advancing fluidly.

Also clarifies the tap hint in all 6 languages to make it explicit
that you need to tap an aircraft (e.g. "Tap an aircraft for more
details" instead of the more ambiguous "Tap for details").

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

src/i18n_en.h

@@ -134,7 +134,7 @@ static const char* const I18N_EN[] = {
     "The device also runs a small web page for exporting the full logbook. While connected to the same WiFi network, open a browser and go to:",
     "No WiFi connection - the export page is only reachable while connected to a network.",
 
-    "Tap for details",
+    "Tap an aircraft for more details",
     "Empty sky for ",
 
     "Model: ",