Add OnlyOffice-based preview for office documents

Replace Aspose.Words with OnlyOffice Document Server for generating
bitmap previews of office documents (Word, Excel, PowerPoint, etc.).

Backend:
- Add cista/onlyoffice.py conversion client
- Convert office docs directly to PNG via OnlyOffice, then AVIF via pyvips
- Make office previews optional based on OnlyOffice availability
- Remove Aspose.Words dependency and all related code
- Add spreadsheet and presentation format support

Frontend:
- Mark office files as previewable in Document.ts
- Add office extensions to MediaPreview.vue preview list
- Fix pre-existing @ts-ignore in HeaderMain.vue

Tests:
- Fix test_lrucache.py parameter name (open -> opener)

Also run ruff format across the codebase to satisfy linter checks.

tests/test_files_path_security.py

@@ -1,4 +1,5 @@
 """Path traversal and percent-encoding security tests for the fileserver."""
+
 from pathlib import Path
 from uuid import uuid4
 
@@ -22,7 +23,13 @@ def setup_storage(tmp_path: Path):
 @pytest_asyncio.fixture()
 async def client(setup_storage: Path):
     app = Sanic(f"files-path-sec-test-{uuid4().hex}", strict_slashes=True)
-    app.router.ALLOWED_METHODS = (*app.router.ALLOWED_METHODS, "MKCOL", "MOVE", "COPY", "PROPFIND")
+    app.router.ALLOWED_METHODS = (
+        *app.router.ALLOWED_METHODS,
+        "MKCOL",
+        "MOVE",
+        "COPY",
+        "PROPFIND",
+    )
     app.blueprint(fileserver_bp)
     yield app.asgi_client