feat(installers): consolidate app installers into host-aware install-apps

Fold macinstaller + install-apt-pkgs + install-tools + install-zellij into a
single host-aware lk-installers/install-apps (macOS->Homebrew, bootstrapping
Homebrew if absent; Linux->apt + upstream installers). Installs the tools the
configs assume (bat, fd, fzf, zoxide, zellij, nvim, btop, htop, tldr) plus the
fzf-git.sh helper and fzf shell integration; idempotent.

link-dotfiles gains --apps to install then link in one shot. .zshrc drops the
redundant brew/system zsh-autosuggestions source (zinit already loads it),
fixing the missing-file error on a fresh box. README documents the new flow.

home_root/.zshrc

@@ -107,10 +107,9 @@ alias cd='z'
 zinit light Aloxaf/fzf-tab
 
 
-if [[ $(uname) == "Darwin" ]]; then
-  source $(brew --prefix)/share/zsh-autosuggestions/zsh-autosuggestions.zsh
-elif [[ $(uname) == "Linux" ]]; then
-  source /usr/share/zsh-autosuggestions/zsh-autosuggestions.zsh
+# zsh-autosuggestions is already loaded via zinit above; on Linux, also wire
+# the terminfo arrow keys to history search.
+if [[ $(uname) == "Linux" ]]; then
   bindkey "${terminfo[kcuu1]}" history-search-backward
   bindkey "${terminfo[kcud1]}" history-search-forward
 fi