* fix(libreoffice): don't force MS Word 97 infilter on .wps
.wps is Microsoft Works, not MS Word 97/.doc. Forcing that infilter
makes soffice reject a genuine Works document with "source file could
not be loaded", even though the same file converts fine when no
--infilter is passed at all (LibreOffice auto-detects it correctly).
Fixes#582
* test: lock in wps export direction; document why null covers both sides
Per review: the filter map feeds both --infilter and the --convert-to
suffix, so wps: null also affects exporting TO wps. That is deliberate
and behavior-preserving: LibreOffice has no Works export filter (its
MS_Works filter is import-only), and bare `--convert-to wps` falls back
to LibreOffice's default export filter for the extension - "MS Word 97",
the exact filter this map pinned before, so export output is unchanged.
Adds a regression test asserting the docx -> wps invocation.
---------
Co-authored-by: tr3lane <182920672+tr3lane@users.noreply.github.com>
dc61643912