feat(tmux): deploy the config on Linux too; prefix i / - splits

- install.sh: deploy_tmux_config runs on both OSes after the bashrc (gated on tmux)
- tmux.conf: clipboard via if-shell (pbcopy on macOS, tmux buffer + OSC 52 elsewhere)
- bashrc-linux exports XDG_CACHE_HOME like the macOS rc files
- prefix i = side-by-side split, prefix - = stacked split (h/j/k/l kept)
- verified in an Ubuntu 24.04 container (tmux 3.4): deploy, bindings, split, plugins, libtmux

CLAUDE.md

@@ -22,7 +22,7 @@ vim/autoload/         pathogen loader (committed)
 vim/colors/           molokai colorscheme (committed)
 bash/bashrc-{linux,osx}          OS-detected bashrc (exports USER/EMAIL identity)
 gitconfig                        user-scope ~/.gitconfig template, @USER@/@EMAIL@ filled at install
-tmux.conf                        tmux config (vi keys, tpm plugins) → ~/.config/tmux/tmux.conf, macOS only
+tmux.conf                        tmux config (vi keys, tpm plugins) → ~/.config/tmux/tmux.conf, both OSes (tmux ≥ 3.1)
 zsh/{zshrc-osx,bchanot.zsh-theme}  macOS zsh option: oh-my-zsh zshrc + theme porting the bash prompt
 bin/{dt,dtach-router,claude-provider}   CLI scripts deployed to ~/.local/bin
 etc/profile.d/disk-usage-warning.sh     login-time low-disk warning → /etc/profile.d (Linux only)