Fix wobbling session-history loading spinner

The "Scanning sessions" loader sat in a `flex items-center gap-2` row
next to a plain text span with no flex-1/min-w-0 sibling to absorb
slack. Both items default to flex-shrink: 1, so the SVG could be
compressed below its 14px width while keeping 14px height — a
non-square box shifts the rotation pivot off center, making the icon
drift instead of spinning in place.

Add `shrink-0`, matching every other text-adjacent spinner in the app.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

src/renderer/src/components/right-sidebar/AiVaultPanelControls.tsx

@@ -76,7 +76,7 @@ export function SessionLoadingState(): React.JSX.Element {
   return (
     <div className="px-3 py-3" aria-busy="true">
       <div className="mb-3 flex items-center gap-2 text-[11px] text-muted-foreground">
-        <LoaderCircle className="size-3.5 animate-spin" />
+        <LoaderCircle className="size-3.5 shrink-0 animate-spin" />
         <span>
           {translate(
             'auto.components.right.sidebar.AiVaultPanelControls.scanningSessions',