Fix preview panel resize soft lock

[Glubus]

Summary

Fixes a UI soft lock that can occur when resizing the online mod preview panel, particularly on Linux/Wayland.

Root cause

The preview panel separator used the native HTML d&d API (draggable and drag events) as a resize mechanism.

On Electron under Wayland, moving the separator could leave the application inside the native d&d interaction. The UI would then stop responding after the panel moved beneath the pointer.

Changes

• Replace native HTML drag-and-drop with pointer events.
• Use pointer capture to keep receiving move and release events during resizing.
• Handle pointer cancellation and lost pointer capture.
• Clamp the panel width to the available layout bounds.
• Prevent invalid panel widths from being persisted.
• Add unit tests for the width-clamping behavior.

Testing

• pnpm typecheck
• pnpm exec vitest run test/vitest/tests/utils/PreviewPanelResizeUtils.spec.ts
• Manually reproduced and verified on EndeavourOS with KDE Wayland.
• Tested using the Risk of Rain 2 online mod preview panel.

Enregistrement.d.ecran_20260812_113303.webm

[CLAassistant]

All committers have signed the CLA.