feat: klines-based simulation instead of polling

- Fetch historical klines once from AVE API (10 CU per request)
- Process each candle as a time step
- Limit to 500 candles max per simulation
- No continuous polling - processes all data in seconds
- Frontend now selects kline interval (1m, 5m, 15m, 1h)
- Much more efficient API usage

src/backend/app/db/schemas.py

@@ -100,7 +100,7 @@ class BacktestResponse(BaseModel):
 class SimulationCreate(BaseModel):
     token: str
     chain: str
-    check_interval: int = 60
+    kline_interval: str = "1m"
 
     @field_validator("chain")
     @classmethod