HEL-373: 主题化 combobox 覆盖夜间下拉全状态，日期面板支持年月直选

原生 select 弹层无法可靠套黑金 token，改为可访问 listbox；日期标题增加年份/月份下拉，越月不提交非法日。

Co-authored-by: Cursor <cursoragent@cursor.com>
Co-authored-by: multica-agent <github@multica.ai>

tests/test_reminders_page.py

@@ -37,7 +37,7 @@ class RemindersPageSourceContractTests(unittest.TestCase):
         self.assertIn('id="reminder-tbody"', html)
         self.assertIn('id="reminder-tabs"', html)
         self.assertIn('id="reminder-detail-drawer"', html)
-        self.assertIn("design-system.css?v=13", html)
+        self.assertIn("design-system.css?v=14", html)
         self.assertIn("app.js?v=18", html)
         pending = html.index('id="pending-reminders-card"')
         history = html.index('id="reminder-history-card"')
@@ -73,7 +73,8 @@ class RemindersPageSourceContractTests(unittest.TestCase):
         self.assertIn(".pick", css)
         self.assertIn("minmax(0, 1.5fr)", css)
         block_start = css.index("提醒管理：三步发送流")
-        block = css[block_start:]
+        block_end = css.index("月结 / 重开 / 审计")
+        block = css[block_start:block_end]
         self.assertIn("var(--border)", block)
         self.assertIn("var(--accent-soft)", block)
         self.assertIn("var(--accent)", block)