fix: carbon fallback, energy history parsing, generation dedup (v1.4.2)

- Carbon overview: fallback to compute from energy_data × emission_factors
  when carbon_emissions table is empty
- Energy history: parse start_time/end_time as datetime (was raw string → 500)
- Dashboard generation: dedup by station prefix to prevent inflated totals
  (93K → 14.8K kWh)
- Realtime window: already at 20min to cover 15min collector interval

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

backend/app/api/v1/energy.py

@@ -32,13 +32,27 @@ async def query_history(
     user: User = Depends(get_current_user),
 ):
     """历史数据查询"""
+    # Parse time strings to datetime for proper PostgreSQL timestamp comparison
+    start_dt = None
+    end_dt = None
+    if start_time:
+        try:
+            start_dt = datetime.fromisoformat(start_time)
+        except ValueError:
+            start_dt = datetime.strptime(start_time, "%Y-%m-%d")
+    if end_time:
+        try:
+            end_dt = datetime.fromisoformat(end_time)
+        except ValueError:
+            end_dt = datetime.strptime(end_time, "%Y-%m-%d").replace(hour=23, minute=59, second=59)
+
     query = select(EnergyData).where(EnergyData.data_type == data_type)
     if device_id:
         query = query.where(EnergyData.device_id == device_id)
-    if start_time:
-        query = query.where(EnergyData.timestamp >= start_time)
-    if end_time:
-        query = query.where(EnergyData.timestamp <= end_time)
+    if start_dt:
+        query = query.where(EnergyData.timestamp >= start_dt)
+    if end_dt:
+        query = query.where(EnergyData.timestamp <= end_dt)
 
     if granularity == "raw":
         query = query.order_by(EnergyData.timestamp.desc()).offset((page - 1) * page_size).limit(page_size)
@@ -74,10 +88,10 @@ async def query_history(
         ).where(EnergyData.data_type == data_type)
         if device_id:
             agg_query = agg_query.where(EnergyData.device_id == device_id)
-        if start_time:
-            agg_query = agg_query.where(EnergyData.timestamp >= start_time)
-        if end_time:
-            agg_query = agg_query.where(EnergyData.timestamp <= end_time)
+        if start_dt:
+            agg_query = agg_query.where(EnergyData.timestamp >= start_dt)
+        if end_dt:
+            agg_query = agg_query.where(EnergyData.timestamp <= end_dt)
         agg_query = agg_query.group_by(text('time_bucket')).order_by(text('time_bucket'))
         result = await db.execute(agg_query)
         return [{"time": str(r[0]), "avg": round(r[1], 2), "max": round(r[2], 2), "min": round(r[3], 2)}