* fix(tool): resolve file_read paths against git top-level in monorepos
ocr review from a monorepo subdirectory failed with "file not found" (#287):
git reports diff and `git show HEAD:<path>` paths relative to the repo root,
but RepoDir was scoped to the invocation subdirectory, producing a double
prefix. resolveWorkingDir now anchors RepoDir at `git rev-parse
--show-toplevel` on the review path (requireGit=true); scan keeps the CWD so
its `git ls-files` walk stays scoped.
The top-level lookup uses a stdout-only git helper so stderr notices can't
pollute the path, and fails loudly if --show-toplevel errors or is empty
(e.g. a bare repo) instead of silently reusing the subdirectory. Adds
regression tests for the subdir hoist, the scan-path scoping, git-show
resolution of root-relative paths, and the bare-repo failure.
* docs(rules): document repo-root rule.json resolution in monorepos
Since #287 anchored RepoDir at the git top-level, ocr review from a
monorepo subdirectory loads the repo-root .opencodereview/rule.json
rather than a subdir-local one. Call out this user-visible behavior at
loadProjectRule so the scope change isn't a surprise (review feedback).
