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

tests/test_nav_files.py

@@ -0,0 +1,49 @@
+# tests/test_nav_files.py — Navigation page listing (#158)
+#
+# The vault home / navigation page lists a directory with its indexed tags so
+# the Vaults · Tags · Extensions facets can filter the listing client-side.
+# The tags must survive the endpoint's response_model.
+from __future__ import annotations
+
+
+def test_vault_files_expose_indexed_tags(client):
+    """Every entry carries a `tags` list; markdown tags come from the index."""
+    resp = client.get("/api/vault/TestVault/files", params={"recursive": False})
+    assert resp.status_code == 200
+
+    data = resp.json()
+    files = data["files"]
+    assert files, "expected a non-empty listing"
+
+    # The field is always present (response_model must not strip it)
+    assert all("tags" in f for f in files)
+
+    by_name = {f["name"]: f for f in files}
+    assert "note1.md" in by_name
+    assert sorted(by_name["note1.md"]["tags"]) == ["python", "tutorial"]
+
+    # Unindexed / tagless files keep an empty list, never null
+    assert sorted(by_name["note2.md"]["tags"]) == ["devops", "docker"]
+    for f in files:
+        assert isinstance(f["tags"], list)
+
+
+def test_vault_files_tags_in_subdirectory(client):
+    """Tags are resolved per directory listing, not only at the vault root."""
+    resp = client.get(
+        "/api/vault/TestVault/files",
+        params={"dir": "Projets", "recursive": False},
+    )
+    assert resp.status_code == 200
+
+    files = resp.json()["files"]
+    by_name = {f["name"]: f for f in files}
+    assert "projet.md" in by_name
+    assert sorted(by_name["projet.md"]["tags"]) == ["projet", "python"]
+
+
+def test_indexed_tags_unknown_vault_returns_empty():
+    """Index miss (unknown vault/file) degrades to an empty tag list."""
+    from backend.services.vaults import _indexed_tags
+
+    assert _indexed_tags("NoSuchVault", "ghost.md") == []