feat: add LLM prediction providers with structured output support

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

app/Services/LlmPrediction/OilPredictionProvider.php

@@ -0,0 +1,18 @@
+<?php
+
+namespace App\Services\LlmPrediction;
+
+use App\Models\BrentPrice;
+use App\Models\PricePrediction;
+use Illuminate\Support\Collection;
+
+interface OilPredictionProvider
+{
+    /**
+     * Generate an oil price direction prediction from recent Brent crude prices.
+     * Returns null on failure, API key not configured, or insufficient data.
+     *
+     * @param  Collection<int, BrentPrice>  $prices  Chronological Brent crude prices
+     */
+    public function predict(Collection $prices): ?PricePrediction;
+}