fix: BigScreen data display, carbon, energy history (v1.6.2)

BigScreen fixes:
- Fix NaN in 今日用电 (normalize energy_today structure)
- Fix 总设备=0 (compute from online+offline)
- Fix energy flow zeros (map total_load→total_power)
- Fix 今日发电=0 (extract from nested energy_today)

Backend fixes (synced from ems-core):
- Carbon overview fallback from energy_data × emission_factors
- Energy history: datetime parsing (was 500)
- Dashboard generation: station-level dedup (93K→14.8K kWh)

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

frontend/src/pages/BigScreen/components/EnergyFlowDiagram.tsx

@@ -20,10 +20,10 @@ export default function EnergyFlowDiagram({ realtime, overview }: Props) {
   const particlesRef = useRef<Particle[]>([]);
   const rafRef = useRef<number>(0);
 
-  const gridPower = realtime?.grid_power ?? 0;
-  const pvPower = realtime?.pv_power ?? 0;
-  const totalPower = realtime?.total_power ?? 0;
-  const hpPower = realtime?.heatpump_power ?? 0;
+  const gridPower = Number(realtime?.grid_power) || 0;
+  const pvPower = Number(realtime?.pv_power) || 0;
+  const totalPower = Number(realtime?.total_power) || Number(realtime?.total_load) || 0;
+  const hpPower = Number(realtime?.heatpump_power) || 0;
 
   useEffect(() => {
     const container = containerRef.current;