Exempt Office/Workspace sidecars from the ignore check

detect() converts Office files and Google Workspace shortcuts into
markdown sidecars under a converted subdirectory of the output dir,
then ran the same scan ignore check on the sidecar's own path. The
documented gitignore advice puts the whole output dir inside a
gitignored tree, so that check rejected the tool's own output for
the same reason a user would gitignore it, and the source document
vanished from the corpus with nothing recorded about why. The check
exists to keep user files out of the scan, not to filter output this
same pass just produced from an already admitted source, so a
sidecar under the converted directory is now exempt from it. Fixes
#3504.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_017qfdzgbA5KedGEjD1AayNh
(cherry picked from commit 900b376d39446ef79dbc60c528c985847fc69389)