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

tests/Feature/Components/FabTest.php

@@ -17,6 +17,14 @@ it('sizes a FAB at 56, 80 and 96px', function (string $size, string $classes, st
     'lg' => ['lg', 'size-24 rounded-corner-xl', 'size-8'],
 ]);
 
+it('fills the FAB\'s glyph, as M3 asks twice over', function () {
+    $svg = trim((string) file_get_contents(__DIR__.'/../../../resources/svg/symbols/filled/add.svg'));
+    $filled = substr($svg, (int) strpos($svg, '><') + 1);
+
+    expect((string) $this->blade('<x-fab icon="add" aria-label="New" />'))->toContain($filled)
+        ->and((string) $this->blade('<x-fab-menu label="New" />'))->toContain($filled);
+});
+
 it('extends with a label', function () {
     expect((string) $this->blade('<x-fab icon="upload" label="Upload" size="md" color="tertiary" variant="filled" />'))
         ->toContain('h-20 min-w-20 gap-3 px-[26px] rounded-corner-lg-increased type-title-lg')