Convert settings from raw text to structured Nix attrs, following
Hyprland's module pattern. Implementation based 1:1 on Hyprland's
design - all credit to the Hyprland project.
- Add nix/lib.nix with toMango conversion function
- Support nested attrs, lists for duplicate keys
- Add extraConfig, topPrefixes, bottomPrefixes options
- Auto-add exec-once for autostart.sh
Adapted for mangowc syntax (underscore separators vs colons).
