shall adopt should discover shell configurations

[SYKhayyat]

Problem

Shell configs (.bashrc, .zshrc, .zshenv, .profile, plugin managers) are a major part of what makes a machine 'this machine', but Shall has no grammar or detection for them. Users must manually write link: lines for each file.

Current behavior

No shell-config-specific grammar. No discovery. Users can use dotfiles: or link: to place shell files, but must identify and declare each one by hand.

Proposed behavior

Detect shell configurations and produce appropriate declarations:

• Shell rc files: .bashrc, .zshrc, .zprofile, .zshenv, .bash_profile, .profile, .config/fish/config.fish
• Plugin managers: oh-my-zsh (\~/.oh-my-zsh), zinit/zplug/zsh-autosuggestions (from .zshrc parsing), nvm/fnm/pyenv/rbenv (version managers)
• Interactive configs: .inputrc, .lesskey, .tmux.conf, .screenrc
• Git config: .gitconfig, .gitignore_global, .config/gh/

Each should map to a link: or dotfiles: declaration pointing to wherever the source lives (dotfiles repo, \~/.config, etc.).

Scope questions

• Plugin managers often install into their own directory (\~/.oh-my-zsh, \~/.nvm). Should adopt scan their contents or just detect their presence?
• Shell configs frequently contain machine-specific paths or secrets. Should adopt redact or skip sensitive lines?
• Should fish/zsh/bash be treated as separate detection scopes or unified?