ui/layout: expand collapsed vertical tabs on hover

[dusan-nikcevic]

• An issue exists where the maintainers agreed that this should be implemented
• I tested that my contribution works locally, and does not break anything
• If my contribution is non-trivial, I did not use AI to write most of it
• I understand that I will be permanently banned from interacting with this organization if I lied by checking any of these checkboxes.

Tested on (check one or more):

• Linux
• Windows
• macOS

---

Closes #915.

This adds an optional hover-expand mode for collapsed vertical tabs.

What changed:

• add a setting to expand collapsed vertical tabs on hover
• expand the collapsed vertical tab strip as an overlay instead of relaying out page content
• keep hover expansion/collapse behavior reliable with delay handling
• avoid hover-triggered expansion while interaction locks are active

Local verification:

• built Helium locally on Linux
• launched the built browser
• manually verified the collapsed vertical sidebar expands on hover

2026-02-27.00-12-54.online-video-cutter.com.mp4

[greptile-apps]

_{Last reviewed commit: 82b073c}