feat(ui): render the language picker as a Vue component

LocalePicker renders the existing picker model with the same markup and
listbox behaviour; ProviderSettingsView shows it while the shell publishes
the active language and its choice handler to the gev-locale store. A host
passing localePicker: false publishes nothing. A choice reaches the shell
after the list is closed on screen, and every opening keeps the active
option in view.

src/ui/styles/locale-picker.css

@@ -1,7 +1,7 @@
 /* ============================================================
    Bottom-right corner row: the POWER UP chip (provider-settings.css)
    and, in the very corner, the interface language picker
-   (src/ui/localePicker.js). Logical properties throughout, so a
+   (src/ui/views/panels/LocalePicker.vue). Logical properties throughout, so a
    right-to-left page mirrors the row and the list.
    ============================================================ */