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/command.h

@@ -403,6 +403,13 @@ enum class user_command
 	wiperswitchincrease,
 	wiperswitchdecrease,
 	lightsset,
+	fmradiotoggle,
+	fmradiovolumeincrease,
+	fmradiovolumedecrease,
+	fmradiovolumeset,
+	fmradiotuneincrease,
+	fmradiotunedecrease,
+	fmradiotuneset,
 	none = -1
 };