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.

scripts/package-boundaries.json

@@ -26,6 +26,7 @@
       "src/ui/views/ContextView.vue",
       "src/ui/views/panels/RadioPanel.vue",
       "src/ui/views/panels/SdrCard.vue",
+      "src/ui/views/panels/PhoneTabBar.vue",
       "src/ui/views/panels/MissionDetail.vue",
       "src/ui/views/panels/MissionRoster.vue",
       "src/ui/views/panels/AwarenessPanel.vue",