Add the M3 date pickers

Docked, modal and modal input date pickers for single dates and ranges,
with locale month names, week start and typed format from Intl, min and
max, and the APG grid keyboard. Completes Phase 7.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01V9NnLxnPp8vaaurb3Z1MFy

resources/css/material.css

@@ -26,6 +26,7 @@
 @import './components/menu.css';
 @import './components/selection.css';
 @import './components/search.css';
+@import './components/datepicker.css';
 @import './components/timepicker.css';
 @import './components/tabs.css';
 @import './components/app-bar.css';