[Bug] Bottom-row rack slot actions are inaccessible on mobile during rack creation

### Describe the bug

When creating a rack on a mobile-sized screen, the action buttons for slots in the bottom row are not accessible.

After tapping a slot in the lowest row, the slot action menu is overlapped by the lower miner-list section. As a result, the buttons such as `Search from list` and `Search miners` are not visible.

### Preconditions

- Use Proto Fleet at a mobile-sized resolution

### Steps to reproduce

1. Open Proto Fleet in a mobile-sized browser viewport
2. Start creating a new rack
3. Enter any rack name and choose any rack size (tested with 2x2, 3x3, 5x1)
4. Continue to the rack layout step
5. Tap any slot in the lowest row of the rack grid

### Expected behavior

The slot action buttons should be fully visible and tappable, including:
- `Search from list`
- `Search miners`

### Actual behavior

The lower section of the screen overlaps the slot action area, and the buttons are not visible at all for slots in the bottom row.

### Proto Fleet version

`nightly-20260703-a7b00e867a12-13-g04a0c8c5-dirty`

### Environment

- OS: macOS
- Browser: Chrome

### Screenshots & screen recordings

https://github.com/user-attachments/assets/093a1e54-2764-4094-a7c1-ab8d3b38ef87

Reproduce the issue in Proto Fleet at a mobile-sized browser viewport, following the rack creation steps through the rack layout step. Focus on the lowest-row slot action menu and verify that its Search from list and Search miners buttons remain visible and tappable without being overlapped by the lower miner-list section.

Written by the indexing model from the issue text.