- shellAliases + initContent replace config/zsh/{zshrc,aliases}
- programs.git.settings replaces config/git/config
- programs.neovim with vimAlias
- mkOutOfStoreSymlink for nvim (lazy-lock.json stays writable)
- platform conditionals: zed alias (darwin), credential.helper (darwin)
- ghistory, pid2port, mern moved to utils as proper functions

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

nix flakes + home-manager for portable shell experience.
strips homebrew/nvm/bun hardcoded paths in favor of nix.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>