A ⌘K palette with no visible entry point is itself a discoverability +
a11y gap (keyboard/SR users can't find it). Added a labeled 'Jump to…'
button (aria-label spells out the shortcut) that dispatches a
'commandpalette:open' event the palette now also listens for. Verified
the other top a11y items are already satisfied here (sonner Toaster
provides the aria-live region; sidebar icon buttons are aria-labeled;
skip-link + drawer focus mgmt already present).