Move the select's rules out of the field into select.css

<x-select> marks its field root data-md-select, and what a <select>
changes in the field — covering the whole box, the customizable
select's closed button, the focused look and turned arrow while open —
moves from field.css to components/select.css (plan step 36). The open
list stays in menu.css until the menu leaves Tailwind.

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

resources/css/components.css

@@ -19,6 +19,7 @@
 @import './components/input.css';
 @import './components/password.css';
 @import './components/textarea.css';
+@import './components/select.css';
 
 /* Containment */