[RGB-loop]

Refs #462. This fixes the refusal half of the issue; two items in its Expected section are not covered (listed under "Not changed").

Problem

A checked workspace.unmount without discard counts every dirty overlay inode. After touch ., touch .probe && rm .probe or mkdir .d && rmdir .d, the overlay holds inode rows a Commit drops, so the unmount is refused Dirty: 0 uncommitted change(s) with changed: [], while workspace.commit answers UpToDate. After a real directory chmod, the change is counted but no path is named, because the probe only names entry rows.

Fix

control/dirty.rs only. The dirty probe now follows Commit's rule for the rows it counts:

• a locally created inode that no name binds any more is skipped (Commit cannot keep it);
• a base directory whose mode equals the base is skipped (Commit ignores a directory's mtime);
• a base directory whose mode differs is named, / for the root.

Files stay conservative: a changed base file is still counted and named, even when only its mtime changed.

Not changed

• A base file whose only change is its mtime (e.g. /.git/index) still refuses the unmount. It is now named, but Commit would drop it.
• list_changes still skips directories that have a local row (operator/workspace.rs), so a directory chmod is named by the refusal but not listed by list_changes. Status counts are unchanged.

Tests

New layerfs-api/tests/unmount_dirty.rs:

• changes_a_commit_drops_do_not_refuse_an_unmount: touch ., touch .git, create+unlink, mkdir+rmdir unmount without discard.
• a_refusal_names_every_change_it_counts: chmod /, chmod /.git, a created file and an index mtime change refuse, naming exactly their path, not truncated.

On main without the dirty.rs change, both fail:

touch .: Dirty(DirtyReport { ..., paths: [], inodes: 1, entries: 0, pending_merge: false, truncated: false })
left: ([], false)    right: (["/"], false)

With it, both pass. Locally (Linux, Rust 1.95.0, Disposable fixture, no mount): cargo fmt --check and the boundary check pass; cargo clippy -p layerfs-daemon --lib -p layerfs-api --test unmount_dirty -- -D warnings passes with -A clippy::result_large_err (on 1.95 that lint fires only in three files this PR does not touch); the other layerfs-daemon / layerfs-api tests that fail here need /dev/fuse, fusectl or cgroups, which this host does not have. Not run locally: the CI toolchain (1.85.1), FUSE end-to-end tests and macOS.

Production LOC: +35 (layerfs-daemon 6,035 -> 6,070).

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