Add the row layout component

Plan step 35: <x-row gap align justify wrap stack-below>, children side
by side in a pane and stacked under one another below an M3 breakpoint,
in the inline direction so a right-to-left document mirrors it.

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

resources/css/layout.css

@@ -7,3 +7,4 @@
 @layer material.reset, material.tokens, material.base, material.layout, material.components, material.text, material.visibility;
 
 @import './layout/stack.css';
+@import './layout/row.css';