Broadcast radio receiver in the cab

Plays internet radio streams (http, mp3) through a positional emitter in the cab, with analog tuning, inter-station noise and two speaker profiles. Stations are listed in fmradio.txt, cab controls are defined with fmradio entries in the .mmd file.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

input/drivermouseinput.cpp

@@ -816,6 +816,15 @@ drivermouse_input::default_bindings() {
 		{ "radiovolumenext_sw:",{
 			radiovolumeincrease,
 			none } },
+		{ "fmradio_sw:",{
+			fmradiotoggle,
+			none } },
+		{ "fmradiovolume_sw:",{
+			fmradiovolumeincrease,
+			fmradiovolumedecrease } },
+		{ "fmradiotune_sw:",{
+			fmradiotuneincrease,
+			fmradiotunedecrease } },
         { "pantfront_sw:", {
             pantographtogglefront,
             none } },