Fill the FAB and icon-button glyphs, and cut small ones at 20

M3 asks a FAB's icon and a default (non-toggle) icon button's icon to be filled,
never outlined; the toggle half of that rule was already right, so only the
`$selected === null` case changed. Every glyph these components draw at 20px now
passes `optical="20"` for the cut M3 draws at that size — button xs/sm, group,
menu item, the alert, snackbar and FAB-menu close buttons, the stat's icon.
Plan step 18, actions.md ACT-14, ACT-15.

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

resources/views/components/fab.blade.php

@@ -9,6 +9,9 @@
      `<div class="fixed end-4 bottom-4"><x-fab icon="add" tooltip="New share" /></div>`. For a
      create action that is a FAB on a phone and a header button above, use `<x-button fab>`.
 
+     The glyph is filled, not outlined: M3 says so twice, in the FAB's anatomy and again in its
+     guidelines ("icon should be filled (not outlined) and unambiguous").
+
      Sizes, corners and elevation from FabBaseline/Medium/LargeTokens and ExtendedFab*Tokens
      (androidx Compose Material 3, Apache-2.0). --}}
 
@@ -65,7 +68,7 @@
 
 <{{ $tag }} {{ $attributes }}>
     @if ($icon)
-        <x-livewire-material::icon :name="$icon" :class="$iconSize" />
+        <x-livewire-material::icon :name="$icon" filled :class="$iconSize" />
     @endif
 
     @if ($extended)