feat(ui): add collapsible advanced settings and enlarge compose modal

Extract a shared forms collapsible for advanced SSH/build settings
across boarding, server creation, and application general. Support
larger modals with header actions, close the compose editor after
save via compose-save-finished, and cover the layout in tests.

resources/views/components/forms/collapsible.blade.php

@@ -0,0 +1,22 @@
+@props([
+    'title' => 'Advanced settings',
+    'contentClass' => '',
+])
+
+<div x-data="{ open: false }" {{ $attributes->class(['flex flex-col gap-4']) }}>
+    <button type="button" x-on:click="open = !open"
+        class="flex items-center gap-2 text-left text-sm font-medium hover:underline" :aria-expanded="open">
+        <svg class="size-4 transition-transform" x-bind:class="open && 'rotate-90'" viewBox="0 0 20 20"
+            fill="currentColor" aria-hidden="true">
+            <path fill-rule="evenodd"
+                d="M7.21 14.77a.75.75 0 0 1 .02-1.06L11.168 10 7.23 6.29a.75.75 0 1 1 1.04-1.08l4.5 4.25a.75.75 0 0 1 0 1.08l-4.5 4.25a.75.75 0 0 1-1.06-.02Z"
+                clip-rule="evenodd" />
+        </svg>
+        {{ $title }}
+    </button>
+
+    <div x-show="open" x-cloak
+        class="rounded-lg border border-neutral-200 p-4 dark:border-coolgray-400 {{ $contentClass }}">
+        {{ $slot }}
+    </div>
+</div>