Add 'Clear All' button for search history

[RemiBonnet]

Regarding this issue #4700

This PR adds a simple "Clear All" button to the search history interface. The button allows users to quickly delete all saved search entries searchHistory and selected profiles selectedProfiles in one action, without introducing unnecessary complexity.

Why this change?

Currently, users must manually delete each search entry one at a time, which can be frustrating. This addition aligns with user expectations and mirrors similar features found in other platforms, like Twitter.

Test plan

1. Confirm the button appears when there is search history to clear.
2. Verify clicking the button removes all entries immediately.
3. Ensure the button disappears when there is no search history.
4. Test the button’s behavior across devices and themes (e.g., light mode).

bluesky-clear-all.mov