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/ui/applicationShell.js

@@ -575,8 +575,6 @@ export class StyleManager extends ShellFacade {
     });
     this._initUI();
     this._initMapStackControl();
-    // Headers first: panel chrome builds its toggle labels from them.
-    this._applyRuntimeStaticHeaderText();
     this._initPanelChrome();
     this._panelNavigation = new PanelNavigation({
       ui: this._ui,
@@ -802,55 +800,6 @@ export class StyleManager extends ShellFacade {
     }
   }
 
-  /**
-   * Rewrites a header's last text node, keeping the leading icon span that a
-   * textContent write would destroy.
-   * @param {Element|null} element
-   * @param {string} text
-   * @returns {void}
-   */
-  _setHeaderText(element, text) {
-    if (!element) return;
-    const textNode = Array.from(element.childNodes)
-      .reverse()
-      .find(
-        (node) => node.nodeType === Node.TEXT_NODE && node.nodeValue?.trim(),
-      );
-    if (textNode) textNode.nodeValue = text;
-    else element.textContent = text;
-  }
-
-  /**
-   * Translates at boot the header texts that share their element with an
-   * icon or a <br> (data-i18n-runtime in the templates).
-   * @returns {void}
-   */
-  _applyRuntimeStaticHeaderText() {
-    this._setHeaderText(
-      document.querySelector('#control-panel .panel-title'),
-      t('VISUAL PRESETS'),
-    );
-    this._setHeaderText(
-      document.querySelector('#location-bar .location-toolbar-label'),
-      t('LOCATION'),
-    );
-    // One span holds both mode descriptions around a <br>; keep the <br>.
-    const standbyDescription = document.querySelector(
-      '#context-mode-standby span',
-    );
-    if (standbyDescription) {
-      standbyDescription.replaceChildren(
-        document.createTextNode(
-          t('CONTACTS — nearest planes · vessels · sites'),
-        ),
-        document.createElement('br'),
-        document.createTextNode(
-          t('SPACE MISSIONS — launches & orbital assets'),
-        ),
-      );
-    }
-  }
-
   /**
    * Phone layout: a bottom tab bar presenting one panel sheet at a time
    * (src/ui/mobileShell.js). Inactive above 720px.