docs: add comprehensive API reference documentation

Adds complete API reference (api-reference.md) covering all endpoints: /api/stations (nearby search with postcode/lat+lng), /api/stats/searches (aggregated search stats), /api/prediction (7-day price forecast with multi-signal breakdown), and auth routes (register/login/logout/me). Includes request/response examples, error shapes, fuel type aliases, and signal structure details. Also removes unused AccountWidget from admin panel, disables BrentPriceChartWidget discovery, and adds searches stat to StatsOverviewWidget.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

app/Filament/Widgets/StatsOverviewWidget.php

@@ -4,6 +4,7 @@ namespace App\Filament\Widgets;
 
 use App\Models\ApiLog;
 use App\Models\PricePrediction;
+use App\Models\Search;
 use App\Models\Station;
 use App\Models\User;
 use Carbon\Carbon;
@@ -18,6 +19,7 @@ class StatsOverviewWidget extends BaseWidget
     {
         return [
             $this->usersStat(),
+			$this->searchesStat(),
             $this->stationsStat(),
             $this->oilPredictionStat(),
             $this->apiErrorsStat(),
@@ -31,6 +33,13 @@ class StatsOverviewWidget extends BaseWidget
             ->color('primary');
     }
 
+	private function searchesStat(): Stat
+	{
+		return Stat::make('Total searches', Search::count())
+			->icon('heroicon-o-magnifying-glass')
+			->color('primary');
+	}
+
     private function stationsStat(): Stat
     {
         $count = Station::count();
@@ -58,8 +67,7 @@ class StatsOverviewWidget extends BaseWidget
         $ageHours = $prediction->generated_at->diffInHours(now());
         $color = $ageHours > 24 ? 'warning' : 'success';
         $value = ucfirst($prediction->direction->value)
-            .' · '.$prediction->confidence.'%'
-            .' · '.strtoupper($prediction->source->value);
+            .' · '.$prediction->confidence.'%';
 
         return Stat::make('Latest oil prediction', $value)
             ->description('Generated '.$prediction->generated_at->diffForHumans())