feat: #152 viewer XLSX — affichage multi-feuilles, édition des cellules et téléchargement des .xlsx

- backend/xlsx_reader.py : rend openpyxl en tableaux HTML (plafond 500x40 par feuille)
- PUT /api/file/{vault}/xlsx/save : service edit_xlsx_cells (backup avant écriture, refs A1 validées)
- frontend : renderXlsxViewer (onglets, contenteditable, sauvegarde par feuille)
- docs : CHANGELOG [Unreleased], Roadmap index #152, archive, README FR/EN, exemple OpenAPI

backend/indexer.py

@@ -65,6 +65,7 @@ SUPPORTED_EXTENSIONS = {
     ".sh", ".bash", ".zsh", ".fish", ".bat", ".cmd", ".ps1",
     ".json", ".yaml", ".yml", ".toml", ".xml", ".csv",
     ".cfg", ".ini", ".conf", ".env", ".pdf",
+    ".xlsx",
     ".html", ".css", ".scss", ".less",
     ".java", ".c", ".cpp", ".h", ".hpp", ".cs", ".go", ".rs", ".rb",
     ".php", ".sql", ".r", ".m", ".swift", ".kt",
@@ -559,6 +560,12 @@ def _scan_vault(
                     raw = ""
                     title = fpath.stem.replace("-", " ").replace("_", " ")
                     content_preview = ""
+                elif ext == ".xlsx":
+                    # #152 — binary workbook: metadata only, the viewer renders
+                    # it (parity with _index_single_file_sync).
+                    raw = ""
+                    title = fpath.stem.replace("-", " ").replace("_", " ")
+                    content_preview = ""
                 else:
                     raw = fpath.read_text(encoding="utf-8", errors="replace")
                     title = fpath.stem.replace("-", " ").replace("_", " ")
@@ -947,6 +954,10 @@ def _index_single_file_sync(vault_name: str, vault_path: str, file_path: str, va
             # #108 — binary media: metadata only, never read the bytes.
             raw = ""
             content_preview = ""
+        elif ext == ".xlsx":
+            # #152 — binary workbook: metadata only (parity with _scan_vault).
+            raw = ""
+            content_preview = ""
         else:
             raw = fpath.read_text(encoding="utf-8", errors="replace")
             content_preview = raw[:200].strip()