feat: broadcast uaux (12V aux battery) on CAN 0x110

Adds AddSend for Param::uaux at CAN ID 0x110, bit 0, length 8, gain=10.
Transmits 12V aux battery voltage in 0.1V steps (e.g. 125 = 12.5V).
VCU reads byte 0 of 0x110 and divides by 10 to get float voltage for
12V battery protection logic.

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

src/chargercan.cpp

@@ -99,4 +99,7 @@ void ChargerCAN::MapMessages(CanMap* can)
    can->AddSend(Param::udc, 0x109, 8, 16, 1);
    can->AddSend(Param::idc, 0x109, 24, 16, 1);
    can->AddSend(Param::opmode, 0x109, 40, 3, 5); //Set charging and connlock at once
+
+   /***** Auxiliary TX *****/
+   can->AddSend(Param::uaux, 0x110, 0, 8, 10); //12V aux battery: byte 0, gain=10 (0.1V resolution)
 }