git status --porcelain collapses an entirely-untracked directory into a
single '?? dir/' entry. collectGitStatus only recurses into such dirs to
find embedded git repos, so source files in a plain untracked directory
were never surfaced to sync — 'codegraph sync' reported 'Already up to
date' and the watcher missed them too.
Add -uall so git lists individual untracked files. Nested untracked git
repos still collapse to '?? repo/' even with -uall (git never crosses a
repo boundary), so the embedded-repo recursion is unaffected.
Export getGitChangedFiles and add regression tests for both the plain
untracked-directory case and the embedded-repo recursion (no -uall
regression).
Root-cause analysis and fix suggested by the reporter in #1213.
