lazyrsync

Added

• rsync_path in settings.toml picks which rsync binary runs instead of the
  first one on $PATH. Useful on macOS 15.4 and later, where /usr/bin/rsync
  is openrsync and shadows Homebrew's rsync, and in any launch context with a
  minimal $PATH such as cron. The configured binary is what the resolved
  command in the TUI and lazyrsync list reports.
• A startup warning when the rsync found on $PATH is older than 3.1. The
  preview needs --itemize-changes, the progress bar needs --info=progress2
  and snapshots need --link-dest; openrsync has none of the first two and
  accepts --link-dest without reliably hardlinking.
• Statically linked musl release binaries for x86_64-unknown-linux-musl and
  aarch64-unknown-linux-musl, so distributions carrying a glibc older than
  2.34 can run a prebuilt binary. cargo binstall resolves them on musl hosts.

Changed

• Saving settings.toml preserves comments and every hand-edited key; only
  hints and last_profile are rewritten. Editing the file while the TUI is
  open no longer loses those edits on exit.
• settings.toml rejects unknown keys, the rule profiles.toml already
  followed. One consequence for both: a file written by a newer lazyrsync may
  fail to load on an older binary rather than being partially ignored.

Fixed

• A settings.toml that exists but cannot be read or parsed is now a loud
  error instead of being silently discarded and replaced with defaults.