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/firstRunExperience.test.mjs

@@ -814,7 +814,7 @@ test('markup, startup ordering and accessibility remain pinned', async () => {
   // passing edit — changing it needs the owner, not a nicer-sounding rewrite.
   assert.ok(
     html.includes(
-      '<p id="first-run-description" data-i18n-runtime>It feels like a forbidden cockpit' +
+      '<p id="first-run-description">It feels like a forbidden cockpit' +
         '—then you realize the sources are public and the data is real.</p>',
     ),
     'the owner-authored first-run line must ship exactly as written',
@@ -903,8 +903,8 @@ test('the card closes without a keyboard: the ESC hint is a button, kept on phon
     footer,
     /<button type="button" class="first-run-dismiss" data-first-run-dismiss>/,
   );
-  assert.match(footer, /data-i18n>ESC to dismiss</);
-  assert.match(footer, /data-i18n>DISMISS</);
+  assert.match(footer, />ESC to dismiss</);
+  assert.match(footer, />DISMISS</);
   // It closes the way ESC does, through the one dismiss path, so the session
   // flag and focus handling are the same: firstRunLauncherView.test.mjs.
   // Phones used to hide the hint, leaving no way out but picking a mission.