Apply restored owners, modes and times in an order that keeps them (closes #219)

A directory got its stored mode and mtime before its contents were
written, so a read-only directory came back without its files and a
non-empty one carried the time of the restore. Directories are now
created owner-only (0700) and get their stored owner, mode and mtime
after the restore loop, each before its parent, skipping any whose
place a symlink has since taken. A file's mode is now applied after its
chown, which on Linux clears setuid and setgid. A symlink gets its
stored owner (as root) and mtime on the link itself, through
golang.org/x/sys/unix, now a direct dependency.

An interrupted restore leaves its directories at 0700.

Model: opus-5-5

go.mod

@@ -24,6 +24,7 @@ require (
 	github.com/stretchr/testify v1.11.1
 	go.uber.org/fx v1.24.0
 	golang.org/x/sync v0.18.0
+	golang.org/x/sys v0.38.0
 	golang.org/x/term v0.37.0
 	gopkg.in/yaml.v3 v3.0.1
 	modernc.org/sqlite v1.38.0
@@ -263,7 +264,6 @@ require (
 	golang.org/x/exp v0.0.0-20251023183803-a4bb9ffd2546 // indirect
 	golang.org/x/net v0.47.0 // indirect
 	golang.org/x/oauth2 v0.33.0 // indirect
-	golang.org/x/sys v0.38.0 // indirect
 	golang.org/x/text v0.31.0 // indirect
 	golang.org/x/time v0.14.0 // indirect
 	golang.org/x/tools v0.38.0 // indirect