refactor(ui): trim header trigger labels and fix dropdown anchoring

OpenInAppButton and ProjectActionsButton now render icon-only triggers in the header instead of icon + text. Padding is tightened accordingly and the now-unused selectedButtonLabel / formatActionButtonLabel helpers are gone.

With narrower triggers the previous center-aligned dropdown with translate -30px started overflowing the viewport on the left edge for ProjectActions. Switched ProjectActions dropdown to align="start" and OpenInApp dropdown to align="end" (matching their positions in the header) and removed the manual translate offset.

Also fixed a long-standing inconsistency where clicking an already-running action in the ProjectActions dropdown re-ran it instead of stopping; the non-compact branch was missing toggleStopIfRunning=true that the compact branch already passed.

MiniChat header now uses bg-sidebar to match the main desktop header palette.

packages/ui/src/components/mini-chat/MiniChatLayout.tsx

@@ -256,7 +256,7 @@ const MiniChatHeader: React.FC<{ mode: MiniChatMode }> = ({ mode }) => {
   return (
     <header
       className={cn(
-        'flex items-center gap-3 border-b border-[var(--interactive-border)] bg-[var(--surface-background)] pr-3',
+        'flex items-center gap-3 border-b border-[var(--interactive-border)] bg-sidebar pr-3',
         hasMacTrafficLights ? 'pl-[5.5rem]' : 'pl-3',
         macosHeaderSizeClass || 'min-h-14',
       )}