feat(ui): render the phone tab bar and sheet backdrop from a store

The phone shell no longer builds its tab bar and backdrop or writes their
aria-expanded, aria-hidden and hidden state: it publishes its tabs,
whether it is on and the open sheet to the gev-display store, and a new
PhoneTabBar component in the dock teleports them to the end of the page
from the first publish until the shell is destroyed, so they still follow
the scene's credits. The shell takes tab and backdrop clicks from the
document and returns focus to a tab once the tab bar shows it closed; a
reopen or destroy cancels a pending return.

docs/VUE-MIGRATION.md

@@ -122,8 +122,12 @@ They contain no application state.
    what `createMapSourceControls()` publishes beside it, so `./ui/maps`
    needs no Vue; the location tray's city and landmark pills, mini status
    and search error render what `LocationControls` publishes to the
-   `gev-location` store, and the search field keeps its listeners),
-   the phone shell, then Cockpit. Layers that write into the right rail
+   `gev-location` store, and the search field keeps its listeners), the
+   phone shell (`PhoneTabBar` renders the tabs and open sheet the shell
+   publishes to the `gev-display` store, teleporting the tab bar and sheet
+   backdrop to the end of the page from the first publish until the shell
+   is destroyed; the shell takes their clicks from the document), then
+   Cockpit. Layers that write into the right rail
    directly gain a slot instead.
 
 4. **Cleanup.** The build-time template expansion and the attribute