refactor(models): extract defaultStandaloneDockerAttributes method on Server

Extract duplicated inline StandaloneDocker attribute arrays in the
Server boot lifecycle into a dedicated method, eliminating repetition
between the root-server (id=0) and normal-server paths.

Also harden the shared_environment_variables migration by wrapping
DDL statements in DB::transaction() and using DROP CONSTRAINT IF EXISTS
to make the migration safely re-runnable.

Add unit test covering the extracted method to verify uuid is always
present in bootstrap attributes.

tests/Unit/ServerBootstrapDestinationAttributesTest.php

@@ -0,0 +1,20 @@
+<?php
+
+use App\Models\Server;
+
+it('includes a uuid in standalone docker bootstrap attributes for the root server path', function () {
+    $server = new Server;
+    $server->id = 0;
+
+    $attributes = $server->defaultStandaloneDockerAttributes(id: 0);
+
+    expect($attributes)
+        ->toMatchArray([
+            'id' => 0,
+            'name' => 'coolify',
+            'network' => 'coolify',
+            'server_id' => 0,
+        ])
+        ->and($attributes['uuid'])->toBeString()
+        ->and($attributes['uuid'])->not->toBe('');
+});