## Summary

In the keymap editor, the search input at the top used `size_full()`
while the
adjacent button row had `min_w_96()`. On narrow panes (e.g. side-by-side
splits), this caused the action buttons — including "Create keybinding"
— to
overflow and clip out of the editor.

This change lets the search input flex and shrink (`flex_1()` +
`min_w_0()`),
and makes the button row `flex_none()` so it keeps its natural width and
stays visible at any pane size.

## Before / After

<img width="2227" height="475" alt="Screenshot 2026-04-23 215511"
src="https://github.com/user-attachments/assets/f3d79922-13e4-486b-b2b0-62ffa5d5b1a2"
/>

## Test plan

- [x] Open the keymap editor (`zed: open keymap editor`)
- [x] Confirm the "Create keybinding" and other action buttons remain
visible
- [x] Confirm the search input shrinks gracefully instead of pushing
buttons off-screen

Co-authored-by: Lukas Wirth <lukas@zed.dev>