## Summary
Fixes the side panel close animation cleanup
(`sidePanelCloseAnimationCompleteCleanup`) never running during the
close transition.
This eventually fixes the issue where in navbar edit mode, clicking on a
nav item sometimes doesn't get selected, the side panel opens but shows
`Select a navigation item to edit` instead of the selected item's
settings. The root cause was stale `isSidePanelClosing` state from a
previous close that wasn't cleaned up, causing the next open to run
cleanup synchronously (without emitting the close event), which
interfered with the navigation item selection flow.
### Root cause
The CSS `transition` on `StyledSidePanelWrapper` used
`${themeCssVariables.animation.duration.normal}s`, which Linaria
converts to a CSS custom property value like `width
var(--t-animation-duration-normal)s`. After CSS variable substitution,
`0.3` and `s` become two separate tokens, not a valid `<time>` dimension
(`0.3s`). The browser rejects the entire transition declaration, falls
back to `all 0s`, and the width change happens instantly with no
`transitionend` event.
### Fix
- Use `calc(var(--t-animation-duration-normal) * 1s)` to properly
construct the `<time>` value (consistent with ~30 other usages in the
codebase).
- Filter `handleTransitionEnd` to only process `width` transitions on
the wrapper element itself, ignoring bubbled child `background-color`
transitions.
## Before
https://github.com/user-attachments/assets/496ccbff-dc96-487d-a994-451dbf2a5165
## After
https://github.com/user-attachments/assets/78255240-1d7d-42cd-9b56-25627613883a
Abdul Rahman
83653a463c