Fix: satisfy mypy and pyrefly for TikaDocumentParser

Use a TYPE_CHECKING-guarded assert to narrow self._tika_client from
TikaClient | None to TikaClient at the point of use in parse().  The
assert is visible to type checkers (TYPE_CHECKING=True) so both mypy
and pyrefly accept the subsequent attribute accesses without error;
at runtime TYPE_CHECKING is False so the assert never executes and no
ruff S101 suppression is required.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

src/paperless/parsers/tika.py

@@ -228,6 +228,9 @@ class TikaDocumentParser:
         documents.parsers.ParseError
             If Tika or Gotenberg returns an error.
         """
+        if TYPE_CHECKING:
+            assert self._tika_client is not None
+
         logger.info("Sending %s to Tika server", document_path)
 
         try: