This simplifies the admin search and adds some basic accessibility

Simplification:

• Removes the filters for now, both in the modal and full-screen
• Removes the link to full-screen from the modal
• Simpler input placeholder text
• Positioned to sit higher on the page, similar to a command palette

Accessibility:

• Results (or lack of) announced for screenreaders after query

Bonus:

• Makes the modal input sticky on scroll
• Combined some styles shared between this and the chat menu (modifier + k) under a --quick-palette class

Before:

After: