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)

database/migrations/2026_04_14_155113_add_prediction_generated_at_to_brent_prices_table.php

@@ -0,0 +1,28 @@
+<?php
+
+use Illuminate\Database\Migrations\Migration;
+use Illuminate\Database\Schema\Blueprint;
+use Illuminate\Support\Facades\Schema;
+
+return new class extends Migration
+{
+    /**
+     * Run the migrations.
+     */
+    public function up(): void
+    {
+        Schema::table('brent_prices', function (Blueprint $table) {
+            $table->timestamp('prediction_generated_at')->nullable()->after('price_usd');
+        });
+    }
+
+    /**
+     * Reverse the migrations.
+     */
+    public function down(): void
+    {
+        Schema::table('brent_prices', function (Blueprint $table) {
+            $table->dropColumn('prediction_generated_at');
+        });
+    }
+};