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>

tests/Feature/Admin/OilPredictionResourceTest.php

@@ -1,27 +0,0 @@
-<?php
-
-use App\Filament\Resources\OilPredictionResource\Pages\ListOilPredictions;
-use App\Models\PricePrediction;
-use App\Models\User;
-use Illuminate\Foundation\Testing\RefreshDatabase;
-use Livewire\Livewire;
-
-uses(RefreshDatabase::class);
-
-beforeEach(function () {
-    $this->admin = User::factory()->admin()->create();
-    $this->actingAs($this->admin);
-});
-
-it('renders the oil prediction list', function () {
-    $predictions = PricePrediction::factory()->count(3)->create();
-
-    Livewire::test(ListOilPredictions::class)
-        ->assertOk()
-        ->assertCanSeeTableRecords($predictions);
-});
-
-it('has a run prediction header action', function () {
-    Livewire::test(ListOilPredictions::class)
-        ->assertActionExists('runPrediction');
-});

tests/Feature/Admin/StatsOverviewWidgetTest.php

@@ -2,10 +2,11 @@
 
 use App\Filament\Widgets\StatsOverviewWidget;
 use App\Models\ApiLog;
-use App\Models\PricePrediction;
 use App\Models\Station;
 use App\Models\User;
+use Carbon\Carbon;
 use Illuminate\Foundation\Testing\RefreshDatabase;
+use Illuminate\Support\Facades\DB;
 use Livewire\Livewire;
 
 uses(RefreshDatabase::class);
@@ -18,7 +19,20 @@ beforeEach(function () {
 it('renders the stats overview widget', function () {
     User::factory()->count(3)->create();
     Station::factory()->count(2)->create();
-    PricePrediction::factory()->create(['generated_at' => now()->subHours(2)]);
+
+    DB::table('weekly_forecasts')->insert([
+        'forecast_for' => now()->next(Carbon::MONDAY)->toDateString(),
+        'model_version' => 'ridge-v1-test',
+        'direction' => 'rising',
+        'magnitude_pence' => 80,
+        'ridge_confidence' => 65,
+        'flagged_duty_change' => false,
+        'reasoning' => 'test',
+        'generated_at' => now()->subHours(2),
+        'created_at' => now(),
+        'updated_at' => now(),
+    ]);
+
     ApiLog::factory()->count(2)->create(['status_code' => 200, 'error' => null, 'created_at' => now()->subMinutes(30)]);
 
     Livewire::test(StatsOverviewWidget::class)