log files should not be world-readable

[notnmeyer]

log files are created with 0644 permissions (world-readable).

problem

$ ls -la ~/.local/share/daylog/default/2025/06/27/log.md
-rw-r--r--  user  group  log.md

if $XDG_DATA_HOME has loose permissions (shared machine, misconfigured umask), anyone can read your personal notes.

fix

use 0600 (owner-only read/write):

// in daylog.go
if err := os.WriteFile(d.Path, content, 0600); err != nil {
    return err
}

directories stay 0755, which is fine.