Remove prediction API endpoint and integrate into stations search

Consolidate prediction functionality by merging /api/prediction endpoint into /api/stations response. Move prediction logic from PredictionController into StationController, returning prediction data alongside station results. Replace usePrediction composable with unified useStations that returns {stations, meta, prediction}. Remove PredictionRequest, related tests, and unused Vue components (FuelFinderTest, MapTest, RecommendationTest, StationListTest). Add PredictionFull component and UpsellBanner. Extend NationalFuelPredictionService to include weekly_summary (7-day series, yesterday/today averages, cheapest/priciest days) and oil signal from price_predictions table. Update Home.vue to consume prediction from stations response. Add Plan::resolveCadenceForUser helper and configure Cashier to use custom Subscription model.

app/Models/Plan.php

@@ -80,6 +80,41 @@ class Plan extends Model
         ]);
     }
 
+    /**
+     * Resolve the active subscription cadence for a user.
+     * Returns 'monthly' | 'annual', or null if the user has no paid subscription.
+     */
+    public static function resolveCadenceForUser(User $user): ?string
+    {
+        if (! method_exists($user, 'subscriptions')) {
+            return null;
+        }
+
+        $priceId = $user->subscriptions()->active()->value('stripe_price');
+
+        if ($priceId === null) {
+            return null;
+        }
+
+        $plan = static::where('stripe_price_id_monthly', $priceId)
+            ->orWhere('stripe_price_id_annual', $priceId)
+            ->first();
+
+        if ($plan === null) {
+            return null;
+        }
+
+        if ($plan->stripe_price_id_monthly === $priceId) {
+            return 'monthly';
+        }
+
+        if ($plan->stripe_price_id_annual === $priceId) {
+            return 'annual';
+        }
+
+        return null;
+    }
+
     protected static function booted(): void
     {
         static::saved(function (): void {