feat: complete i18n coverage — all dynamic content translated

All remaining French strings converted to t() calls:
- ui.js: create/delete file/dir modals, rename/copy/bookmark toasts
- palette.js: confirm dialogs, error toasts
- search.js: result summary text with interpolation
- config.js: about/diagnostics section labels
- auth.js: admin panel title
- viewer.js: forge popout labels
- dashboard.js: shared widget buttons, date locale-aware

57 new locale keys for dynamic content (modals, toasts, admin, about)
Total: 597 keys per language

All 26 modules validated — 163 exports, 0 errors

frontend/js/config.js

@@ -875,7 +875,7 @@ function renderDiagnostics(container, data) {
     {
       title: "Index",
       rows: [
-        ["Fichiers indexés", data.index.total_files],
+        [t("about.files_indexed"), data.index.total_files],
         ["Tags uniques", data.index.total_tags],
         ["Vaults", Object.keys(data.index.vaults).join(", ")],
       ],
@@ -927,34 +927,34 @@ function loadAbout() {
     
     const sections = [
       {
-        title: "Application",
+        title: t("about.section_app"),
         rows: [
-          ["Nom", "ObsiGate"],
-          ["Version", state.APP_VERSION],
-          ["Version API", health.version || "—"],
-          ["Statut", health.status || "—"],
+          [t("about.name"), "ObsiGate"],
+          [t("about.version"), state.APP_VERSION],
+          [t("about.api_version"), health.version || "—"],
+          [t("about.status"), health.status || "—"],
         ],
       },
       {
-        title: "Environnement",
+        title: t("about.section_env"),
         rows: [
-          ["Vaults configurés", health.vaults || "—"],
-          ["Fichiers indexés", health.total_files || "—"],
-          ["Navigateur", navigator.userAgent.split(" ").pop()],
-          ["Plateforme", navigator.platform || "—"],
-          ["Langue", navigator.language || "—"],
+          [t("about.vaults_configured"), health.vaults || "—"],
+          [t("about.files_indexed"), health.total_files || "—"],
+          [t("about.browser"), navigator.userAgent.split(" ").pop()],
+          [t("about.platform"), navigator.platform || "—"],
+          [t("about.language"), navigator.language || "—"],
         ],
       },
       {
-        title: "Composants",
+        title: t("about.section_components"),
         rows: [
-          ["Backend", "FastAPI (Python)"],
-          ["Rendu Markdown", "mistune"],
-          ["Surveillance fichiers", "watchdog"],
-          ["Frontend", "Vanilla JavaScript"],
-          ["Icônes", "Lucide Icons"],
-          ["Coloration syntaxe", "highlight.js"],
-          ["Éditeur", "CodeMirror 6"],
+          [t("about.backend"), "FastAPI (Python)"],
+          [t("about.markdown_renderer"), "mistune"],
+          [t("about.file_watcher"), "watchdog"],
+          [t("about.frontend"), "Vanilla JavaScript"],
+          [t("about.icons"), "Lucide Icons"],
+          [t("about.syntax_highlight"), "highlight.js"],
+          [t("about.editor"), "CodeMirror 6"],
         ],
       },
     ];