chore: retire legacy oil prediction pipeline

Removes everything that was made redundant by the new forecasting
stack. Per docs/superpowers/specs/2026-05-01-prediction-rebuild-design.md,
this was the cleanup planned at the end of Phase 4.

Deleted services and code:
- App\Services\Prediction\Signals\* (the old six-signal aggregator —
  trend, supermarket, day-of-week, brand-behaviour, stickiness,
  regional-momentum, oil — replaced by RidgeRegressionModel).
- App\Services\NationalFuelPredictionService (the post-Phase-4 thin
  shim; StationSearchService now depends on WeeklyForecastService
  directly, set up in the previous commit).
- App\Services\LlmPrediction\* (AbstractLlmPredictionProvider plus
  the four provider implementations — Anthropic, OpenAI, Gemini, and
  the OilPredictionProvider router. Replaced by LlmOverlayService).
- App\Services\BrentPricePredictor and App\Services\Ewma. The Ewma
  helper had no callers left after BrentPricePredictor went.
- App\Models\PricePrediction and its factory.
- App\Console\Commands\PredictOilPrices (the oil:predict command).
- App\Filament\Resources\OilPredictionResource and its Pages.

Schema and dashboard:
- Drop the price_predictions table via a new migration.
- Repoint the Filament StatsOverviewWidget tile from PricePrediction
  to WeeklyForecast so the dashboard reflects the new pipeline.
- Remove the OilPredictionProvider binding from AppServiceProvider.

Test cleanup:
- Delete tests for every retired service.
- Update StatsOverviewWidgetTest to seed weekly_forecasts instead of
  price_predictions.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

app/Providers/AppServiceProvider.php

@@ -4,11 +4,6 @@ namespace App\Providers;
 
 use App\Listeners\HandleStripeWebhook;
 use App\Models\Subscription;
-use App\Services\ApiLogger;
-use App\Services\LlmPrediction\AnthropicPredictionProvider;
-use App\Services\LlmPrediction\GeminiPredictionProvider;
-use App\Services\LlmPrediction\OilPredictionProvider;
-use App\Services\LlmPrediction\OpenAiPredictionProvider;
 use Carbon\CarbonImmutable;
 use Illuminate\Support\Facades\Date;
 use Illuminate\Support\Facades\DB;
@@ -25,15 +20,9 @@ class AppServiceProvider extends ServiceProvider
      */
     public function register(): void
     {
-        $this->app->bind(OilPredictionProvider::class, function ($app) {
-            $logger = $app->make(ApiLogger::class);
-
-            return match (config('services.llm.provider')) {
-                'openai' => new OpenAiPredictionProvider($logger),
-                'gemini' => new GeminiPredictionProvider($logger),
-                default => new AnthropicPredictionProvider($logger),
-            };
-        });
+        // No bindings here. The legacy LLM prediction provider binding
+        // was removed when the Phase 4 ridge model + Phase 8
+        // LlmOverlayService replaced the old daily oil prediction.
     }
 
     /**