feat: add version API and solar KPI endpoint (v1.4.0)

New endpoints:
- GET /api/v1/version — returns VERSIONS.json (no auth required)
  For field engineers to check platform version from login page
- GET /api/v1/kpi/solar — returns PR, self-consumption rate,
  equivalent utilization hours, and daily revenue
  Handles station-level vs device-level data deduplication

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

backend/app/api/v1/kpi.py

@@ -0,0 +1,93 @@
+from datetime import datetime, timezone
+from fastapi import APIRouter, Depends
+from sqlalchemy.ext.asyncio import AsyncSession
+from sqlalchemy import select, func, and_
+from app.core.database import get_db
+from app.core.deps import get_current_user
+from app.models.device import Device
+from app.models.energy import EnergyData
+from app.models.user import User
+
+router = APIRouter(prefix="/kpi", tags=["关键指标"])
+
+
+@router.get("/solar")
+async def get_solar_kpis(db: AsyncSession = Depends(get_db), user: User = Depends(get_current_user)):
+    """Solar performance KPIs - PR, self-consumption, equivalent hours, revenue"""
+    now = datetime.now(timezone.utc)
+    today_start = now.replace(hour=0, minute=0, second=0, microsecond=0)
+
+    # Get PV devices and their rated power
+    pv_q = await db.execute(
+        select(Device.id, Device.rated_power).where(
+            Device.device_type.in_(["pv_inverter", "sungrow_inverter"]),
+            Device.is_active == True,
+        )
+    )
+    pv_devices = pv_q.all()
+    pv_ids = [d[0] for d in pv_devices]
+    total_rated_kw = sum(d[1] or 0 for d in pv_devices)  # kW
+
+    if not pv_ids or total_rated_kw == 0:
+        return {
+            "pr": 0, "self_consumption_rate": 0,
+            "equivalent_hours": 0, "revenue_today": 0,
+            "total_rated_kw": 0, "daily_generation_kwh": 0,
+        }
+
+    # Get latest daily_energy per PV device for today
+    daily_gen_q = await db.execute(
+        select(
+            EnergyData.device_id,
+            func.max(EnergyData.value).label("max_energy"),
+        ).where(
+            and_(
+                EnergyData.timestamp >= today_start,
+                EnergyData.data_type == "daily_energy",
+                EnergyData.device_id.in_(pv_ids),
+            )
+        ).group_by(EnergyData.device_id)
+    )
+
+    # Check if values are station-level (all identical) or device-level
+    daily_values = daily_gen_q.all()
+    if not daily_values:
+        daily_generation_kwh = 0
+    else:
+        values = [row[1] or 0 for row in daily_values]
+        # If all values are identical, it's station-level data — use max (not sum)
+        if len(set(values)) == 1 and len(values) > 1:
+            daily_generation_kwh = values[0]
+        else:
+            daily_generation_kwh = sum(values)
+
+    # Performance Ratio (PR) = actual output / (rated capacity * peak sun hours)
+    # Approximate peak sun hours from time of day (simplified)
+    hours_since_sunrise = max(0, min(12, (now.hour + now.minute / 60) - 6))  # approx 6am sunrise
+    theoretical_kwh = total_rated_kw * hours_since_sunrise * 0.8  # 0.8 = typical irradiance factor
+    pr = (daily_generation_kwh / theoretical_kwh * 100) if theoretical_kwh > 0 else 0
+    pr = min(100, round(pr, 1))  # Cap at 100%
+
+    # Self-consumption rate (without grid export meter, assume 100% self-consumed for now)
+    # TODO: integrate grid export meter data when available
+    self_consumption_rate = 100.0
+
+    # Equivalent utilization hours = daily generation / rated capacity
+    equivalent_hours = round(daily_generation_kwh / total_rated_kw, 2) if total_rated_kw > 0 else 0
+
+    # Revenue = daily generation * electricity price
+    # TODO: get actual price from electricity_pricing table
+    # Default industrial TOU average price in Beijing: ~0.65 CNY/kWh
+    avg_price = 0.65
+    revenue_today = round(daily_generation_kwh * avg_price, 2)
+
+    return {
+        "pr": pr,
+        "self_consumption_rate": round(self_consumption_rate, 1),
+        "equivalent_hours": equivalent_hours,
+        "revenue_today": revenue_today,
+        "total_rated_kw": total_rated_kw,
+        "daily_generation_kwh": round(daily_generation_kwh, 2),
+        "avg_price_per_kwh": avg_price,
+        "pv_device_count": len(pv_ids),
+    }