~/.mempalace/tunnels.json (introduced in #790) was created via plain
open(..., "w") with no chmod, and its parent dir via os.makedirs()
without mode=0o700. On Linux with default umask 022 both end up
world-readable (0o644 / 0o755).
Tunnels reveal cross-wing connections — which projects, people, and
rooms the user has explicitly linked — so they are sensitive metadata
that should not be readable by other local users on shared systems.
Apply the same 0o700 / 0o600 pattern that #814 established for the
other sensitive palace files. Chmod calls are wrapped in try/except
(OSError, NotImplementedError) for Windows / unsupported-filesystem
compatibility.
Closes#1165
Arnold Wender