i18n: complete audit — 55 new keys, all hardcoded strings converted to t()

- Added 4 missing keys: button.cancel, toast.dir_renamed, toast.file_deleted, toast.file_renamed
- Replaced 41 hardcoded showToast() strings with t() calls across 13 JS files
- Replaced 10 hardcoded textContent/title/innerHTML strings with t() calls
- Fixed theme labels: Sombre/Clair -> t('theme.dark')/t('theme.light')
- Fixed vault selector: Tous les vaults -> t('help.all_vaults')
- Both locale files: 983 -> 1032 keys, perfectly matched
- Bidirectional EN<->FR switching verified in browser

frontend/js/search.js

@@ -984,7 +984,7 @@ export function renderAdvancedSearchResults(data, query, tagFilter) {
           exclude_paths: exclEl?.value || "",
         }),
       });
-      showToast("Recherche sauvegardée", "success");
+      showToast(t("search.saved"), "success");
       loadSavedSearches();
     } catch (err) { showToast("Erreur: " + err.message, "error"); }
   });
@@ -1128,7 +1128,7 @@ export function renderAdvancedSearchResults(data, query, tagFilter) {
   if (data.total > state.ADVANCED_SEARCH_LIMIT) {
     const paginationDiv = el("div", { class: "search-pagination" });
     const prevBtn = el("button", { class: "search-pagination__btn", type: "button" });
-    prevBtn.textContent = "← Précédent";
+    prevBtn.textContent = t('search.previous');
     prevBtn.disabled = state.advancedSearchOffset === 0;
     prevBtn.addEventListener("click", () => {
       state.advancedSearchOffset = Math.max(0, state.advancedSearchOffset - state.ADVANCED_SEARCH_LIMIT);