Add pricing-page waitlist (name + email signup)

Replaces the disabled "Coming soon" buttons on the pricing page with a
waitlist band so visitors can be notified when alerts launch — separate
from registered users.

- waitlist_subscribers table (name, email unique, source, referrer)
- WaitlistService::subscribe — normalises email, idempotent
- Public POST /api/waitlist (throttle:10,1), thin controller + form request
- Read-only Filament resource with streamed CSV export
- Vue: useWaitlist composable + WaitlistForm, rendered below the grid
  while any tier is still "coming soon"; sends source + document.referrer

Announcement send mechanism deferred to a later task.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

routes/api.php

@@ -5,6 +5,7 @@ use App\Http\Controllers\Api\AuthController;
 use App\Http\Controllers\Api\StationController;
 use App\Http\Controllers\Api\StatsController;
 use App\Http\Controllers\Api\UserController;
+use App\Http\Controllers\Api\WaitlistController;
 use App\Http\Middleware\VerifyApiKey;
 use Illuminate\Support\Facades\Cache;
 use Illuminate\Support\Facades\Route;
@@ -22,6 +23,9 @@ Route::get('/fuel-types', function () {
 
 Route::get('/stats/live', [StatsController::class, 'live']);
 
+// Feature-launch waitlist signup (public, separate from registered users)
+Route::post('/waitlist', [WaitlistController::class, 'store'])->middleware('throttle:10,1');
+
 // Protected endpoints (API key required)
 Route::middleware(['throttle:60,1', VerifyApiKey::class])->group(function (): void {
     Route::get('/stations', [StationController::class, 'index']);