Ease a collapse open, which its own comment already promised

Plan step 19, containment.md C-24. `interpolate-size: allow-keywords`
was set and nothing transitioned, so the content snapped open. A new
resources/css/components/collapse.css transitions `block-size` on
`::details-content` over the fast spatial spring, with
`content-visibility` `allow-discrete` beside it so the section stays
rendered while it closes. The `<details>` carries `data-collapse` for
the rule to find.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01Qwx5USif3wFFmxtHg5U1g9

resources/views/components/collapse.blade.php

@@ -5,7 +5,8 @@
      and is announced as a disclosure. Drawn in M3's terms: a title-medium `title` (or a
      `heading` slot), an optional leading `icon`, a chevron that turns over on the spatial spring,
      and — where the browser supports animating `details` content (`interpolate-size`) — a height
-     that eases open. `open` starts it open. `variant`: `plain` (the default, on the surface around
+     that eases open on the same spring (`data-collapse`, resources/css/components/collapse.css).
+     `open` starts it open. `variant`: `plain` (the default, on the surface around
      it) or `filled` (a surface-container tile with a large corner).
 
      Its open state can be bound, both ways:
@@ -38,6 +39,7 @@
 
 <details
     wire:ignore.self
+    data-collapse
     @if ($bound)
         x-data="{ collapseOpen: @if ($model !== null) @entangle($attributes->wire('model')) @else @js($expanded) @endif }"
         @if ($model === null) x-modelable="collapseOpen" @endif