G1000 MFD EIS: real two-bus volts, alternator/battery amps, engine hours

- electrical readout now shows M (main) and E (essential) bus volts from
  bus_volts[0]/[1], M (alternator generator_amps) and S (battery_amps) separately,
  and ENG hours from flight time — replacing the hardcoded duplicate volts / +0.0
  amps / 0.0 HRS placeholders (manual S.54 C172 layout)

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

server/config.js

@@ -96,8 +96,10 @@ export const DATAREFS = {
   oilPress:    'sim/cockpit2/engine/indicators/oil_pressure_psi',
   egt:         'sim/cockpit2/engine/indicators/EGT_deg_C',
   fuelQty:     'sim/cockpit2/fuel/fuel_quantity',
-  volts:       'sim/cockpit2/electrical/bus_volts',
-  amps:        'sim/cockpit2/electrical/battery_amps',
+  volts:       'sim/cockpit2/electrical/bus_volts',     // array: [0]=main bus, [1]=essential
+  amps:        'sim/cockpit2/electrical/battery_amps',  // battery (S) amps
+  genAmps:     'sim/cockpit2/electrical/generator_amps', // alternator (M) amps
+  engHrs:      'sim/time/total_flight_time_sec',         // proxy for engine/tach hours
 
   // --- autopilot readouts (live values, so the panel reflects reality) ---
   apState:     'sim/cockpit2/autopilot/autopilot_state',        // bitfield of active modes