i18n: translate the application views with t() as they render

Every data-i18n, data-i18n-title, data-i18n-aria-label and
data-i18n-placeholder marker in the Vue templates becomes a t() call with
the key the boot pass used to look up, contexts included. The three labels
the shell rewrote at boot (Visual Presets, Location and the standby
description) render through t() too, and that rewrite is gone. With the
locale in vue-i18n, view text now follows a locale change, and markup
under v-if or v-for no longer comes back in English when it re-renders.

Rendered text and attributes are unchanged in every locale. The boot pass
still translates static page markup such as the loading screen and a host's
own markup, and npm run i18n rejects data-i18n* in a Vue template.

src/mapStackChips.test.mjs

@@ -336,7 +336,7 @@ test('the Visual Presets tray owns Map Source and the retired left panel is abse
   );
   assert.match(
     html,
-    /<section class="map-source-section"[\s\S]*?<div id="map-stack-chips" class="map-stack-chip-row" role="group" aria-label="Map source" data-i18n-aria-label><\/div>/,
+    /<section class="map-source-section"[\s\S]*?<div id="map-stack-chips" class="map-stack-chip-row" role="group" aria-label="Map source"><\/div>/,
   );
   assert.doesNotMatch(
     html,