fix: respect candle_delay from config, default to fast tests

- Tests now run with candle_delay=0 for fast execution
- Simulation defaults to candle_delay based on interval (e.g., 30s for 1m)
- Progress saved to DB every 5 seconds during simulation
- User can now see real-time updates while simulation runs

Tests: 14 passing in 0.15s

src/backend/app/db/schemas.py

@@ -119,6 +119,9 @@ class SimulationResponse(BaseModel):
     signals: Optional[List[dict]]
     klines: Optional[List[dict]] = None  # Price data for chart
     trade_log: Optional[List[dict]] = None  # Trade activity log
+    current_candle_index: Optional[int] = None  # Progress: current candle
+    total_candles: Optional[int] = None  # Progress: total candles
+    candles_processed: Optional[int] = None  # Progress: candles processed
 
     class Config:
         from_attributes = True