fix(ui): app header overflow on mobile (#14704)

### What?
If the step nav's content is too long, then it will overflow the screen
on mobile devices. Instead, this portion of the header should grow and
shrink as needed, rather than being the full width of the header.

### Why?
I believe this issue was introduced with a change to the menu button.

### How?

- remove `width: 100%` as it is inaccurate to the desired size
- add `min-width: 0` to allow it to shrink
- change `flex-grow: 1` to `flex: 1` to make it take up the available
space

Before:

<img width="374" height="41"
alt="{D5255587-F9A4-494B-B1CE-DE350C550E6F}"
src="https://github.com/user-attachments/assets/5e2f3a4b-08c8-499b-8211-bed83d44e808"
/>

After:

<img width="374" height="37"
alt="{77C3D92D-DC0F-431B-8001-11B21754290C}"
src="https://github.com/user-attachments/assets/24fc034b-051b-4888-898e-83a98949d1fc"
/>

Author: 6TELOIV

packages/ui/src/elements/AppHeader/index.scss

@@ -91,8 +91,8 @@
     &__controls-wrapper {
       display: flex;
       align-items: center;
-      flex-grow: 1;
-      width: 100%;
+      flex: 1;
+      min-width: 0;
     }
 
     &__step-nav-wrapper {