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/Console/Commands/PredictOilPrices.php

@@ -1,58 +0,0 @@
-<?php
-
-namespace App\Console\Commands;
-
-use App\Services\BrentPricePredictor;
-use Illuminate\Console\Command;
-use Throwable;
-
-class PredictOilPrices extends Command
-{
-    protected $signature = 'oil:predict {--force : Generate even if the latest price already has a prediction}';
-
-    protected $description = 'Generate a Brent crude oil price direction prediction';
-
-    public function handle(BrentPricePredictor $predictor): int
-    {
-        try {
-            $latest = $predictor->latestPrice();
-
-            if ($latest?->prediction_generated_at !== null && ! $this->option('force')) {
-                $message = sprintf(
-                    'Prediction already generated for %s at %s.',
-                    $latest->date->toDateString(),
-                    $latest->prediction_generated_at->toDateTimeString(),
-                );
-
-                if (! $this->confirm($message.' Run again anyway?', default: false)) {
-                    $this->info('Skipped.');
-
-                    return self::SUCCESS;
-                }
-            }
-
-            $this->info('Generating prediction...');
-            $prediction = $predictor->generatePrediction();
-
-            if ($prediction === null) {
-                $this->error('Could not generate a prediction — not enough price data.');
-
-                return self::FAILURE;
-            }
-
-            $this->info(sprintf(
-                'Done. [%s] direction=%s confidence=%d%% — %s',
-                strtoupper($prediction->source->value),
-                $prediction->direction->value,
-                $prediction->confidence,
-                $prediction->reasoning,
-            ));
-        } catch (Throwable $e) {
-            $this->error("Prediction failed: {$e->getMessage()}");
-
-            return self::FAILURE;
-        }
-
-        return self::SUCCESS;
-    }
-}