Remove macOS window-chrome (traffic-light dots, minimize taskbar)

Strip the whole window metaphor as UI baggage: the traffic-light dots
injected at the top of every page, the minimize taskbar, and the
minimize/maximize state and all their CSS. windowChrome.js and taskbar.js
are gone; the only structural DOM the shell still does — wrapping the
takeover Dashboard in .aurora-dashboard-frame and reparenting its notices
into the card — moved to a focused dashboardFrame.js (initDashboardFrame()).

SiteShell.vue drops the taskbar rendering/state; shell-frame.css drops the
.aurora-winbar*/.aurora-taskbar*/minimized/maximized rules and the
--aurora-taskbar-h / --aurora-editor-winbar-h vars, and zeroes the editor
and theme-install frame offsets that reserved a top strip for the dots.
shell.js 16.4->13.4 kB. The editor "back to list" crumb lived in the bar
and was removed with it (Gutenberg's own W-logo still navigates back).

Co-Authored-By: Claude Opus 4.8 <[email protected]>

app/src/pages/dashboard/components/AuroraCard.vue

@@ -31,7 +31,7 @@ defineProps({
   flex-direction: column;
   height: 100%;
   /* Deeper than the generic --aurora-card-bg — the Dashboard is now
-     wrapped in its own frame (windowChrome.js's .aurora-dashboard-frame,
+     wrapped in its own frame (dashboardFrame.js's .aurora-dashboard-frame,
      using --aurora-frame-bg), and that's close in tone to --aurora-card-bg
      for most presets, so cards would nearly disappear into it otherwise. */
   background: var(--aurora-card-bg-deep, var(--aurora-card-bg));