feat(watcher): add scrollback history logging on window/pane close

Introduces watcher.py — a kitty Python watcher that captures terminal
scrollback to ~/.terminal_history/ whenever any window or pane is closed
via Ctrl+D, keybind, or full kitty quit. Works alongside the fish
smart_exit function, which handles graceful shell exits and sets a
user var flag to prevent duplicate logs.

Fixes the kitty.conf watcher directive (removed invalid --type=global
prefix that caused a FileNotFoundError on every kitty startup).

kitty.conf

@@ -11,6 +11,10 @@ notify_on_cmd_finish never
 copy_on_select yes
 # }}}
 
+# {{{ Watcher
+watcher watcher.py
+# }}}
+
 # {{{ Window
 remember_window_size no
 initial_window_width 150c