Add flight route lookup, helicopter marker, and QR code for WebUI

Detail panel now shows origin/destination via adsbdb.com callsign
lookup. Rotorcraft (ADS-B category A7) get a distinct rotor-cross
marker instead of a heading arrowhead, same rationale as the existing
ground-vehicle marker. WebUI info screen gets a QR button (when WiFi
is connected) that renders the local WebUI URL as a scannable code.

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

src/radar_screen.h

@@ -12,7 +12,7 @@ namespace RadarScreen {
     // aus, nicht per Antippen auf dem Radar) - damit beim naechsten render()
     // sofort das Detail-Panel fuer dieses Flugzeug erscheint, so als haette
     // man es direkt im Radar angetippt.
-    void selectAircraft(const char* hex);
+    void selectAircraft(const char* hex, const char* callsign);
 
     struct EmergencyInfo {
         bool active = false;