feat(админка): middleware UseAdminConnection — swap default на pgsql_admin

Меняет default-подключение на pgsql_admin на время admin-запроса и
восстанавливает прежнее в finally (важно для Pest: несколько запросов в
одном процессе). Ставится после saas-admin. Tests: swap+restore и
restore при исключении downstream.

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

app/tests/Unit/Middleware/UseAdminConnectionTest.php

@@ -0,0 +1,42 @@
+<?php
+
+declare(strict_types=1);
+
+use App\Http\Middleware\UseAdminConnection;
+use Illuminate\Http\Request;
+use Illuminate\Support\Facades\DB;
+use Tests\TestCase;
+
+uses(TestCase::class);
+
+it('switches default connection to pgsql_admin during the request', function () {
+    $original = DB::getDefaultConnection();
+    $seen = null;
+
+    $response = (new UseAdminConnection())->handle(
+        Request::create('/api/admin/tenants'),
+        function () use (&$seen) {
+            $seen = DB::getDefaultConnection();
+
+            return response('ok');
+        }
+    );
+
+    expect($seen)->toBe('pgsql_admin');
+    expect($response->getContent())->toBe('ok');
+    expect(DB::getDefaultConnection())->toBe($original); // восстановлено
+});
+
+it('restores the default connection even when downstream throws', function () {
+    $original = DB::getDefaultConnection();
+
+    $call = fn () => (new UseAdminConnection())->handle(
+        Request::create('/api/admin/tenants'),
+        function () {
+            throw new RuntimeException('boom');
+        }
+    );
+
+    expect($call)->toThrow(RuntimeException::class);
+    expect(DB::getDefaultConnection())->toBe($original);
+});