feat(issues): sticky mini bar for agent live card + toast icon colors

Agent live card now uses the sentinel pattern to detect when it scrolls
out of view. When stuck, it collapses to a compact header bar with brand
styling and backdrop blur, with a ChevronUp button to scroll back.
When scrolled back into view, the card seamlessly expands to full view.

Also adds semantic colors to Sonner toast icons (success/info/warning/
error/loading) and fixes icon-to-text alignment in toasts globally.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

apps/web/components/ui/sonner.tsx

@@ -13,19 +13,19 @@ const Toaster = ({ ...props }: ToasterProps) => {
       className="toaster group"
       icons={{
         success: (
-          <CircleCheckIcon className="size-4" />
+          <CircleCheckIcon className="size-4 text-success" />
         ),
         info: (
-          <InfoIcon className="size-4" />
+          <InfoIcon className="size-4 text-info" />
         ),
         warning: (
-          <TriangleAlertIcon className="size-4" />
+          <TriangleAlertIcon className="size-4 text-warning" />
         ),
         error: (
-          <OctagonXIcon className="size-4" />
+          <OctagonXIcon className="size-4 text-destructive" />
         ),
         loading: (
-          <Loader2Icon className="size-4 animate-spin" />
+          <Loader2Icon className="size-4 animate-spin text-brand" />
         ),
       }}
       style={