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_webdav.py

@@ -1,4 +1,5 @@
 """WebDAV protocol tests: OPTIONS, PROPFIND, PROPPATCH, COPY, MOVE, LOCK, UNLOCK."""
+
 import xml.etree.ElementTree as ET
 from pathlib import Path
 from uuid import uuid4
@@ -113,9 +114,7 @@ async def test_propfind_file_has_content_length(client, setup_storage: Path):
 
 @pytest.mark.asyncio
 async def test_propfind_depth_infinity_rejected(client, setup_storage: Path):
-    _, res = await client.request(
-        "PROPFIND", "/files/", headers={"Depth": "infinity"}
-    )
+    _, res = await client.request("PROPFIND", "/files/", headers={"Depth": "infinity"})
     assert res.status_code == 403