fix(email): Mobile scheduled send

[evanhutnik]

Summary

• Fix scheduled send date picker positioning on mobile: In the reply compose (BaseInput), the date picker modal now renders inline (without a portal) on mobile so it shifts up correctly with the compose box when the keyboard opens. The Compose page retains the portal behavior since it needs to escape overflow containers.
• Fix touch selection on mobile: Added onPointerDown with preventDefault on date picker items and the "Clear" button to prevent input blur from closing the combobox before the selection click event fires.
• Close modal on date selection: The date picker now closes automatically after selecting a date/time or pressing "Clear", instead of staying open.
• Compact mode on mobile: On mobile, the date selector trigger only shows the clock icon (no date text) to save space. The icon is colored with the accent color when a scheduled time is set. On desktop, the full date text with accent background pill is preserved.

[github-actions]

Preview: https://evan-scheduled-send-mobile-zbvyr5.preview.macro.com/app (a63cc93)