i18n: fix hardcoded French in Statistics and Shortcuts panel

- dashboard.js: Fichiers/Tags uniques/Taille totale/Vaults -> t() calls
- config.js: Tags uniques/Vaults in About -> t() calls
- index.html: Raccourcis & Astuces -> data-i18n
- Added 5 new keys: dashboard.stats_*, help.shortcuts_title

frontend/js/config.js

@@ -876,8 +876,8 @@ function renderDiagnostics(container, data) {
       title: "Index",
       rows: [
         [t("about.files_indexed"), data.index.total_files],
-        ["Tags uniques", data.index.total_tags],
-        ["Vaults", Object.keys(data.index.vaults).join(", ")],
+        [t("dashboard.stats_tags"), data.index.total_tags],
+        [t("dashboard.stats_vaults"), Object.keys(data.index.vaults).join(", ")],
       ],
     },
     {

frontend/js/dashboard.js

@@ -34,10 +34,10 @@ const DashboardStatsWidget = {
     if (!grid) return;
     const fmtSize = (bytes) => bytes < 1024 ? `${bytes} o` : bytes < 1048576 ? `${(bytes/1024).toFixed(1)} Ko` : bytes < 1073741824 ? `${(bytes/1048576).toFixed(1)} Mo` : `${(bytes/1073741824).toFixed(1)} Go`;
     const items = [
-      { icon: "files", label: "Fichiers", value: data.total_files.toLocaleString() },
-      { icon: "tags", label: "Tags uniques", value: data.total_tags.toLocaleString() },
-      { icon: "hard-drive", label: "Taille totale", value: fmtSize(data.total_size_bytes) },
-      { icon: "folder-open", label: "Vaults", value: data.vaults.length.toString() },
+      { icon: "files", label: t('dashboard.stats_files'), value: data.total_files.toLocaleString() },
+      { icon: "tags", label: t('dashboard.stats_tags'), value: data.total_tags.toLocaleString() },
+      { icon: "hard-drive", label: t('dashboard.stats_size'), value: fmtSize(data.total_size_bytes) },
+      { icon: "folder-open", label: t('dashboard.stats_vaults'), value: data.vaults.length.toString() },
     ];
     grid.innerHTML = items.map(i => `
       <div class="stat-card">