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

tmux.conf

@@ -139,14 +139,12 @@ bind -n C-k if-shell "$is_vim" "send-keys C-k" "select-pane -R"
 
 bind Escape copy-mode                              # bind vi-like 'normal' mode
 bind -Tcopy-mode-vi 'v' send -X begin-selection    # bind vi-like visual mode
-bind -Tcopy-mode-vi 'y' send -X copy-pipe-and-cancel "pbcopy"       # macOS copy
-bind p run "pbpaste | tmux load-buffer - ; tmux paste-buffer"      # macOS paste
-# bind vi-like copy/paste through 'normal' mode, (Note) {{{
-#   Linux (X11) variant, xsel rather than xclip: xclip does not close STDOUT
-#   after reading tmux's buffer, so tmux waits for it and hangs.
-#  bind -Tcopy-mode-vi 'y' send -X copy-pipe-and-cancel "xsel -b -i"
-#  bind p run "xsel -b -o | tmux load-buffer - ; tmux paste-buffer"
-# }}}
+# Clipboard: pbcopy/pbpaste on macOS. Elsewhere tmux's own buffer, which tmux
+# also hands to the terminal through OSC 52 (set-clipboard), so it reaches the
+# local clipboard over ssh. xsel/xclip dropped: headless servers have no X.
+if-shell 'command -v pbcopy >/dev/null' \
+    'bind -Tcopy-mode-vi y send -X copy-pipe-and-cancel pbcopy ; bind p run "pbpaste | tmux load-buffer - ; tmux paste-buffer"' \
+    'bind -Tcopy-mode-vi y send -X copy-selection-and-cancel ; bind p paste-buffer'
 bind-key -Tcopy-mode-vi Escape send -X cancel                  # cancel v mode
 bind-key -Tcopy-mode-vi ^v send -X rectangle-toggle            # cancel v mode
 
@@ -164,6 +162,8 @@ bind-key k "split-window -v -b -c '#{pane_current_path}'"
 bind-key h "split-window -h -b -c '#{pane_current_path}'"
 bind-key j "split-window -v -c '#{pane_current_path}'"
 bind-key l "split-window -h -c '#{pane_current_path}'"
+bind-key i "split-window -h -c '#{pane_current_path}'"   # i: side by side (vertical bar)
+bind-key - "split-window -v -c '#{pane_current_path}'"   # -: stacked (horizontal bar)
 
 bind q kill-window                         # Kill window
 bind Q kill-session                        # Kill the session (not server)