Put the menu on M3's Expressive spacing and behaviour

Items were 44px tall with the baseline menu's 12px sides, the separator had half
its 8dp padding, a disabled item was skipped by the keyboard entirely, a chosen
item was told by colour and shape alone, and the list simply faded in place. Now:
48px rows with 16px either side, an 8px separator, disabled items focusable but
never activatable, a trailing check on a selected item, and an enter-exit that
scales the list out of the corner nearest its trigger — the scale on the spatial
spring, the fade on the effects one. Plan step 18, actions.md ACT-11, ACT-12,
ACT-13, ACT-26, ACT-27, ACT-28.

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

resources/views/components/menu-separator.blade.php

@@ -1,3 +1,4 @@
-{{-- A line between groups of items in an `<x-menu>`. --}}
+{{-- A line between groups of items in an `<x-menu>`: 1px, with M3's 8px above and below it, inset
+     to the 16px the items keep either side. --}}
 
-<hr role="separator" {{ $attributes->class('mx-3 my-1 h-px border-0 bg-outline-variant') }} />
+<hr role="separator" {{ $attributes->class('mx-4 my-2 h-px border-0 bg-outline-variant') }} />