[Xoppyc]

Summary

Makes the side detail panes in both the Ownership Tree (component details) and the Reactivity Graph (node details) horizontally resizable.

Changes

1. ResizeHandle & useResizableDetail primitive:

   • Built a reusable ResizeHandle in src/ui.
   • Uses ::before for a generous 12px invisible grab hitbox, and ::after for the visual indicator.
   • Clean visual states: subtle semi-transparent line on hover (opacity: 0.6), expanding to a solid 3px accent line while dragging (no glow/blur).
   • Double-clicking the resize handle resets width back to default (320px).
   • Width is clamped between 240px and 70% viewport width and persisted in localStorage.

2. Panel Integrations:

   • Wired into <aside data-solid-ownership-detail> in OwnershipViewer.
   • Wired into <aside data-solid-reactivity-detail> in ReactivityViewer.

3. Tests & Changeset:

   • Added unit test in use-resizable-detail.test.ts.
   • Added E2E test in devtools.spec.ts verifying drag resize and double-click reset.
   • Added changeset.

[lxsmnsyc]

Thanks, this is small and fits the existing panels. CI passed. One behavior issue and a few nits.

Should fix

1. The edge drifts away from the pointer after hitting a limit. ResizeHandle reports the delta since the last pointermove, and onResizeDelta adds it to the already clamped width. Drag 100px past the minimum, then back 50px: the panel grows 50px while the pointer is still 50px past the edge. Fix: record the start width and start X on pointerdown and set width = startWidth + (startX - clientX), clamped.

Nits

• The maximum is 70% of window.innerWidth, but the panel also has the 11rem sidebar. At a 1000px window the tree gets about 120px. Clamping to the panel's own width would keep the tree usable. A window resize also does not re-clamp the saved width.
• Both panels share one storage key, so resizing one resizes the other. If that is intended, a short comment would help.
• The Reactivity detail was 19rem (304px) and now defaults to 320px.
• role="separator" without tabindex and aria-valuenow cannot be used from the keyboard. Arrow-key resizing would fix that.

This PR and #41 both change src/dev-toolbar/ownership/index.tsx and conflict there; whichever merges second needs a rebase.