1.0.0-rc.4

Release candidate patch for ArtifactFS 1.0.

This supersedes 1.0.0-rc.3 and includes the git status performance work from PR #26.

Changes since 1.0.0-rc.3:

- Speed up `git status` on ArtifactFS mounts by avoiding full clean worktree walks through FUSE.
- Add `ReadDirPlus` support so directory listings can return child attributes without per-entry lookup.
- Configure a repo-local fsmonitor hook for managed gitdirs and enable fsmonitor on macFUSE with `fsmonitor.allowRemote=true`.
- Report exact dirty overlay paths from the fsmonitor hook so a single modified file does not dirty a whole subtree.
- Mark index entries fsmonitor-clean only after HEAD generation and runtime state are updated.
- Fix fsmonitor test portability.

Verification:

- GitHub PR #26 checks passed: Build & Test, CodeQL, and Semgrep.
- Local release validation from merged `origin/main`: `go build ./cmd/artifact-fs`, `go vet ./...`, `go test ./...`, and `go run golang.org/x/tools/go/analysis/passes/modernize/cmd/modernize@latest -fix ./... && git diff --exit-code`.