refactor: split oil price ingestion and prediction into separate services + commands

- BrentPriceFetcher owns ingestion (fetchFromEia / fetchFromFred, each throws on failure)
- BrentPricePredictor owns prediction and marks latest brent_prices row as generated
- oil:fetch command tries EIA, falls back to FRED, fails loudly if both fail
- oil:predict command prompts if latest price already has a prediction; --force bypasses
- add prediction_generated_at column to brent_prices
- delete OilPriceService (replaced by the two focused services)

app/Models/BrentPrice.php

@@ -6,9 +6,8 @@ use Database\Factories\BrentPriceFactory;
 use Illuminate\Database\Eloquent\Attributes\Fillable;
 use Illuminate\Database\Eloquent\Factories\HasFactory;
 use Illuminate\Database\Eloquent\Model;
-use Illuminate\Support\Carbon;
 
-#[Fillable(['date', 'price_usd'])]
+#[Fillable(['date', 'price_usd', 'prediction_generated_at'])]
 class BrentPrice extends Model
 {
     /** @use HasFactory<BrentPriceFactory> */
@@ -27,6 +26,7 @@ class BrentPrice extends Model
         return [
             'date' => 'date',
             'price_usd' => 'decimal:2',
+            'prediction_generated_at' => 'datetime',
         ];
     }
 }