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.

cista/util/lrucache.py

@@ -58,7 +58,9 @@ class LRUCache:
         Expire items that are either too old or exceed cache capacity.
         """
         ts = monotonic() - self.maxage
-        while len(self.cache) > self.capacity or (self.cache and self.cache[-1][2] < ts):
+        while len(self.cache) > self.capacity or (
+            self.cache and self.cache[-1][2] < ts
+        ):
             self.cache.pop()[1].close()
 
     def close(self):