Speak the editor in each person's Home Assistant language: every text in the editor section of en.json, the mockup in the screens' language, and one Language & region card for all screens

- vue-i18n 11 with the Composition API: English comes with the page, any other language loads the first time it is
  needed from screen_manager/translations, and a text a language lacks shows in English. The build keeps only _meta
  and editor of each file (vite.config.ts), never the screens' or the add-on's texts.
- The editor follows the language of the user's Home Assistant profile (<html lang> of Home Assistant's page), else
  the browser's; plural forms follow the file's _meta.plural, with the screens' rules.
- Every request tells the add-on the editor's language (X-ESP-Screens-Language), so its own words can follow it.
- The mockup draws the screens' words (Unavailable, Page 2 ›, the date, "5 min ago") in the screens' language, with
  their clock and number format.
- Settings → Language & region: the screen language, time format and number format for every screen, with the user's
  own profile offered when it differs. The per-screen clock choice goes; the top bar points there. A screen that
  still needs the new language says so in its update badge.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

web/vite.config.ts

@@ -1,5 +1,20 @@
 import vue from "@vitejs/plugin-vue";
-import { defineConfig } from "vite";
+import { defineConfig, type Plugin } from "vite";
+
+// Every language is one file in screen_manager/translations (app 0.2.90), shared with the firmware and the add-on. The
+// page needs only the language itself (_meta) and the editor's texts: the screens' and the add-on's texts stay out of
+// the build. Before Vite's own JSON step, so the modules it makes hold these two sections only.
+export function editorTexts(): Plugin {
+  return {
+    name: "esp-screens-editor-texts",
+    enforce: "pre",
+    transform(code, id) {
+      if (!/[\\/]screen_manager[\\/]translations[\\/][^\\/?]+\.json$/.test(id)) return null;
+      const { _meta, editor } = JSON.parse(code);
+      return { code: JSON.stringify({ _meta, editor }), map: null };
+    },
+  };
+}
 
 // The add-on serves the built page from screen_manager/app/static behind Home Assistant ingress,
 // which lives on a sub path with a token. Everything is relative so the page works there and on
@@ -7,7 +22,14 @@ import { defineConfig } from "vite";
 // files change. `npm run dev` proxies /api to a running server (the demo home or SCREEN_DEV).
 export default defineConfig({
   base: "./",
-  plugins: [vue()],
+  plugins: [editorTexts(), vue()],
+  // vue-i18n's switches (app 0.2.90): the Composition API only, texts compiled in the page, no devtools in the build.
+  define: {
+    __VUE_I18N_FULL_INSTALL__: true,
+    __VUE_I18N_LEGACY_API__: false,
+    __INTLIFY_PROD_DEVTOOLS__: false,
+    __INTLIFY_DROP_MESSAGE_COMPILER__: false,
+  },
   build: {
     outDir: "../screen_manager/app/static",
     emptyOutDir: false,
@@ -16,5 +38,7 @@ export default defineConfig({
   server: {
     port: 5173,
     proxy: { "/api": { target: "http://127.0.0.1:8099", changeOrigin: false } },
+    // The translations live beside the add-on, outside web/.
+    fs: { allow: [".", "../screen_manager/translations"] },
   },
 });