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
