Add comprehensive test coverage and update notes

tests/Unit/StatsControllerUnitTest.php

@@ -0,0 +1,63 @@
+<?php
+
+use App\Http\Controllers\StatsController;
+use App\Models\Setting;
+use Illuminate\Support\Facades\Storage;
+use Illuminate\Support\Facades\DB;
+
+it('returns null board version when no version is set', function (): void {
+    Setting::where('key', 'version')->delete();
+    Setting::where('key', 'build')->delete();
+
+    $controller = new StatsController();
+    $response = $controller->__invoke();
+    $payload = $response->getData(true);
+
+    expect($payload['board_version'])->toBeNull();
+});
+
+it('handles stats edge cases without crashing', function (): void {
+    Storage::fake('public');
+
+    Setting::updateOrCreate(['key' => 'version'], ['value' => '1.0.0']);
+    Setting::updateOrCreate(['key' => 'build'], ['value' => '9']);
+
+    DB::shouldReceive('connection->getDriverName')->andReturn('sqlite');
+    DB::shouldReceive('selectOne')->andThrow(new RuntimeException('db fail'));
+
+    $controller = new StatsController();
+    $response = $controller->__invoke();
+
+    $payload = $response->getData(true);
+
+    expect($payload['database_size_bytes'])->toBeNull();
+    expect($payload['database_server'])->toBeNull();
+    expect($payload['board_version'])->toBe('1.0.0 (build 9)');
+    expect($payload['orphan_attachments'])->toBeInt();
+});
+
+it('returns null for database size and avatar size on exceptions', function (): void {
+    DB::shouldReceive('connection->getDriverName')->andThrow(new RuntimeException('db fail'));
+
+    $controller = new StatsController();
+    $refDb = new ReflectionMethod($controller, 'resolveDatabaseSize');
+    $refDb->setAccessible(true);
+    $refAvatar = new ReflectionMethod($controller, 'resolveAvatarDirectorySize');
+    $refAvatar->setAccessible(true);
+
+    expect($refDb->invoke($controller))->toBeNull();
+    \Illuminate\Support\Facades\Storage::shouldReceive('disk')->andThrow(new RuntimeException('disk fail'));
+    expect($refAvatar->invoke($controller))->toBeNull();
+});
+
+it('sums avatar directory size', function (): void {
+    Storage::fake('public');
+    Storage::disk('public')->put('avatars/a.png', 'a');
+    Storage::disk('public')->put('avatars/b.png', 'bb');
+
+    $controller = new StatsController();
+    $refAvatar = new ReflectionMethod($controller, 'resolveAvatarDirectorySize');
+    $refAvatar->setAccessible(true);
+
+    expect($refAvatar->invoke($controller))->toBe(3);
+});