perf: increase render interval on static screens from 300ms to 2000ms

Static screens (SettingsScreen, BotScreen, FullscreenMsgView, message
list, contact picker) were re-rendering every 300ms with no visible
benefit. New messages still trigger immediate refresh via newMsg() →
_next_refresh=100, so responsiveness is unchanged. Reduces unnecessary
SPI transfers and CPU wakeups ~6x on idle static screens.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

examples/companion_radio/ui-new/FullscreenMsgView.h

@@ -85,7 +85,7 @@ struct FullscreenMsgView {
       display.setCursor(display.width() - 6, nav_y);
       display.print(">");
     }
-    return 300;
+    return 2000;
   }
 
   Result handleInput(char c) {