feat: onglet de navigation avec facettes, tris et retour Home complet #158

- clic sur un repertoire de l'arbre (modes focus vault et All) ouvre un onglet de navigation dedie qui coexiste avec les onglets de fichiers ouverts
- vue: sous-repertoires cliquables, facettes Vaults/Tags/Extensions (meme mecanisme que la recherche), tris Pertinence/Date, bouton Sauver; tags indexes exposes par GET /api/vault/{v}/files
- BUG-100: showWelcome re-injecte la section Raccourcis & Astuces et goHome efface la recherche globale + le filtre de la sidebar

frontend/js/ui.js

@@ -2105,6 +2105,41 @@ export const TabManager = {
     this.activate(tabId);
   },
 
+  /** Open (or retarget) the navigation tab for a vault directory (#158).
+   *  One navigation tab per vault: clicking another directory reuses it and
+   *  updates its directory, so open file tabs are never displaced. */
+  async openNav(vault, dir = "") {
+    if (!vault || vault === "all") return;
+    dir = dir || "";
+    const tabId = `nav::${vault}`;
+    const name = dir ? dir.split("/").pop() : vault;
+
+    const existing = this._tabs.find(t => t.id === tabId);
+    if (existing) {
+      existing.path = dir;
+      existing.name = name;
+      this._tabCache[tabId].path = dir;
+      this._tabCache[tabId].title = name;
+      // Force a re-render when it is already the active tab
+      if (this._activeTabId === tabId) this._activeTabId = null;
+      this._renderTabs();
+      this.activate(tabId);
+      return;
+    }
+
+    this._tabs.push({ id: tabId, vault, path: dir, name, icon: "folder", nav: true });
+    this._tabCache[tabId] = { vault, path: dir, title: name, data: null, rawSource: null, sourceView: false, scrollTop: 0, icon: "folder", nav: true };
+    this._renderTabs();
+    this.activate(tabId);
+  },
+
+  /** Drop the active-tab marker — the dashboard/home page is showing.
+   *  Keeps the tabs open; clicking one re-activates (and re-renders) it. */
+  deactivate() {
+    this._activeTabId = null;
+    this._renderTabs();
+  },
+
   /** Activate a specific tab */
   async activate(tabId) {
     if (this._activeTabId === tabId && this._tabs.length > 0) return;
@@ -2125,6 +2160,18 @@ export const TabManager = {
     const cache = this._tabCache[tabId];
     if (!cache) return;
 
+    // Navigation tab — render the directory view instead of fetching a file
+    if (cache.nav) {
+      state.currentVault = cache.vault;
+      state.currentPath = cache.path || null;
+      const navMod = await import("./vaulthome.js");
+      await navMod.showVaultHome(cache.vault, cache.path);
+      if (history.pushState) {
+        history.pushState(null, "", `#/nav/${encodeURIComponent(cache.vault)}/${encodeURIComponent(cache.path)}`);
+      }
+      return;
+    }
+
     // Update global state
     state.currentVault = cache.vault;
     state.currentPath = cache.path;