feat: show real-time download progress bar for app updates

Leverage the Tauri updater plugin's DownloadEvent callback to display
a progress bar with downloaded/total bytes during app updates, replacing
the previous spinner-only feedback.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

src/i18n/messages/ar.json

@@ -172,6 +172,7 @@
     "checking": "جارٍ التحقق...",
     "checkUpdate": "التحقق من التحديثات",
     "updating": "جارٍ التثبيت...",
+    "downloading": "جارٍ التنزيل...",
     "upgradeTo": "الترقية إلى v{version}",
     "foundUpdate": "تم العثور على إصدار جديد v{version}",
     "alreadyLatest": "أنت على أحدث إصدار",

src/i18n/messages/de.json

@@ -172,6 +172,7 @@
     "checking": "Wird geprüft...",
     "checkUpdate": "Nach Updates suchen",
     "updating": "Wird installiert...",
+    "downloading": "Herunterladen...",
     "upgradeTo": "Auf v{version} aktualisieren",
     "foundUpdate": "Neue Version v{version} gefunden",
     "alreadyLatest": "Du verwendest bereits die neueste Version",

src/i18n/messages/en.json

@@ -172,6 +172,7 @@
     "checking": "Checking...",
     "checkUpdate": "Check for updates",
     "updating": "Installing...",
+    "downloading": "Downloading...",
     "upgradeTo": "Upgrade to v{version}",
     "foundUpdate": "New version v{version} found",
     "alreadyLatest": "You're on the latest version",

src/i18n/messages/es.json

@@ -172,6 +172,7 @@
     "checking": "Comprobando...",
     "checkUpdate": "Buscar actualizaciones",
     "updating": "Instalando...",
+    "downloading": "Descargando...",
     "upgradeTo": "Actualizar a v{version}",
     "foundUpdate": "Nueva versión v{version} encontrada",
     "alreadyLatest": "Ya tienes la versión más reciente",

src/i18n/messages/fr.json

@@ -172,6 +172,7 @@
     "checking": "Vérification...",
     "checkUpdate": "Rechercher les mises à jour",
     "updating": "Installation...",
+    "downloading": "Téléchargement...",
     "upgradeTo": "Mettre à jour vers v{version}",
     "foundUpdate": "Nouvelle version v{version} trouvée",
     "alreadyLatest": "Vous utilisez déjà la dernière version",

src/i18n/messages/ja.json

@@ -172,6 +172,7 @@
     "checking": "確認中...",
     "checkUpdate": "更新を確認",
     "updating": "インストール中...",
+    "downloading": "ダウンロード中...",
     "upgradeTo": "v{version} にアップグレード",
     "foundUpdate": "新しいバージョン v{version} が見つかりました",
     "alreadyLatest": "すでに最新バージョンです",

src/i18n/messages/ko.json

@@ -172,6 +172,7 @@
     "checking": "확인 중...",
     "checkUpdate": "업데이트 확인",
     "updating": "설치 중...",
+    "downloading": "다운로드 중...",
     "upgradeTo": "v{version}로 업그레이드",
     "foundUpdate": "새 버전 v{version}을 찾았습니다",
     "alreadyLatest": "이미 최신 버전입니다",

src/i18n/messages/pt.json

@@ -172,6 +172,7 @@
     "checking": "Verificando...",
     "checkUpdate": "Verificar atualizações",
     "updating": "Instalando...",
+    "downloading": "Baixando...",
     "upgradeTo": "Atualizar para v{version}",
     "foundUpdate": "Nova versão v{version} encontrada",
     "alreadyLatest": "Você já está na versão mais recente",

src/i18n/messages/zh-CN.json

@@ -172,6 +172,7 @@
     "checking": "检查中...",
     "checkUpdate": "检查更新",
     "updating": "升级中...",
+    "downloading": "下载中...",
     "upgradeTo": "升级到 v{version}",
     "foundUpdate": "发现新版本 v{version}",
     "alreadyLatest": "当前已经是最新版本",

src/i18n/messages/zh-TW.json

@@ -172,6 +172,7 @@
     "checking": "檢查中...",
     "checkUpdate": "檢查更新",
     "updating": "升級中...",
+    "downloading": "下載中...",
     "upgradeTo": "升級到 v{version}",
     "foundUpdate": "發現新版本 v{version}",
     "alreadyLatest": "目前已是最新版本",