Adds the portal's top-left app switcher to the editor sidebar, so you
can jump between the two apps from either side.
- Both sidebars render the same shared `AppSwitch` component (sui
dropdown).
- Switching is client-side (no page reload); portal→editor no longer
breaks when `VITE_EDITOR_URL` is unset.
- Editor side is admin-gated (`portalAccess`) and only exists in flavors
that ship the portal — core/desktop stub it out, same seam pattern as
the portal routes.
- Fixes en route: dropdown menu stacking in the editor sidebar, sui
dropdown item button reset, stale `dist-portal` ESLint ignore.
