- Extract package autoimport logic into 5pkgs/flake-module.nix
- Support both package.nix (preferred) and default.nix
- Show deprecation warning when using default.nix

- Replace symlinkJoin with custom multiOutputSymlinkJoin that correctly handles multi-output packages
- Preserve man pages, docs, and other outputs by symlinking from original package outputs
- Fix zsh build while maintaining access to man pages via .man output
- All wrapper tools (mpv, mutt, zsh) now build successfully with full output preservation

- Add passthru parameter to makeWrapper for custom attributes
- Convert mutt to use passthru instead of manual attribute merging
- This simplifies the code and makes wrapper configuration cleaner

Replace writeShellApplication with makeWrapper:
- Set NOTMUCH_CONFIG environment variable directly
- Pass muttrc via -F flag
- Remove obsolete mutt.sh script

Replace writeShellApplication with makeWrapper using flagSeparator="="
to generate the --flag=value format that mpv requires