- Add Go `EmailParser` support for Outlook `.msg` (OLE2/CFB) files via
the `gomsg` library, in addition to the existing `.eml` (RFC 5322)
support. The `.msg` hard-error is gone; emails with `.msg` attachments
are now ingested end-to-end.
- Re-chunk email attachments into retrievable text (user-oriented). Each
attachment is re-parsed by its file extension through the shared parser
registry and folded back into the same document, so attachment content
becomes searchable. This mirrors Python's legacy `rag/app/email.py`.
Binary attachments (images/audio/video/folders) are skipped by design.
- Restore a corrupted `sample.msg` test fixture and add guards so binary
fixtures are never mangled again (`.gitattributes` marks `*.msg` binary;
`check_files.py` skips NUL-byte files). Also made `check_files.py`
ruff-clean.
