Fix side panel open/close animation glitches in the page header and panel content (#22598)

When the side panel opens or closes, the pinned header button (e.g. New
Company) was flat-clipped for the whole 300ms animation: the ⋮ toggle
mounts instantly and shifts the button's slot, framer's `layout` prop
compensates with a transform that the surrounding `overflow: hidden`
containers don't follow, and the ResizeObserver-driven rerenders re-seed
that transform every frame. Removing `layout` lets the button follow
plain reflow, which cannot clip.

The panel content also squeezed during the animation (labels
re-truncating at every intermediate width) because the inner panel was
`width: 100%` of the width-animating wrapper. Pinning it to
`var(--side-panel-width)` turns the animation into a rigid drawer slide;
drag-resize is unaffected since it writes the same CSS variable.

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packages/twenty-front/src/modules/command-menu-item/display/components/PinnedCommandMenuItemButtons.tsx

@@ -73,7 +73,6 @@ export const PinnedCommandMenuItemButtons = () => {
               {pinnedInlineCommandMenuItems.map((item) => (
                 <StyledCommandMenuItemContainer
                   key={item.id}
-                  layout
                   initial={{ width: 0, opacity: 0 }}
                   animate={{ width: 'unset', opacity: 1 }}
                   exit={{ width: 0, opacity: 0 }}

packages/twenty-front/src/modules/side-panel/components/SidePanelForDesktop.tsx

@@ -44,7 +44,7 @@ const StyledSidePanel = styled.aside`
   height: 100%;
   overflow: hidden;
   position: relative;
-  width: 100%;
+  width: var(${SIDE_PANEL_WIDTH_VAR});
 `;
 
 const StyledModalContainer = styled.div`