feat(c5): add zellij exit-capture logging and shared prune helper

Zellij has no live-stream facility like tmux pipe-pane, so capture is a
one-shot 'zellij action dump-screen --full' run from a fish_exit handler
(conf.d/zellij-logging.fish -> functions/_zellij_dump_log.fish). The C5
guard is checked inside the helper at exit time, so toggling logging
needs no sync_logging coordination — there is no persistent stream.

Extract pruning into functions/_prune_terminal_logs.fish, shared by both
the tmux and zellij helpers. This also fixes a latent bug in the tmux
helper: globbing tmux_*.log directly errored with 'No matches for
wildcard' on the first log in an empty dir. The shared helper globs via
'set' (tolerates no-match) and uses command ls/rm to bypass the eza and
trash C1 shadows.

README.md

@@ -178,7 +178,7 @@ If you'd rather set them by hand, each category is controlled by a universal var
 | `__fish_config_op_autoexec` | Startup side-effects: Fisher bootstrap, theme apply, `paru`/`yay` wrapper generation, auto venv activation, WakaTime hook |
 | `__fish_config_op_overrides` | Vi mode, `exit`→`smart_exit`, `$PAGER`/`$MANPAGER`/`$CDPATH`, bang-bang history expansion, autopair, puffer, Starship prompt, theme colors |
 | `__fish_config_op_integrations` | Kitty/WezTerm window abbreviations, `done` notifications, `spwin`/`tab`/`split`, `hist`, `logs`, `upgrade`, WakaTime |
-| `__fish_config_op_logging` | Scrollback capture on exit, tmux `pipe-pane` pane logging, `paru`/`yay` AUR log wrappers, Kitty watcher capture (sentinel-file coordinated) |
+| `__fish_config_op_logging` | Scrollback capture on exit, tmux `pipe-pane` pane logging, zellij `dump-screen` capture on exit, `paru`/`yay` AUR log wrappers, Kitty watcher capture (sentinel-file coordinated) |
 | `__fish_config_op_greeting` | Per-session `fish_greeting` (suppresses distro greetings such as CachyOS fastfetch by overriding with an empty function); first-run welcome banner |
 | `__fish_config_opinionated` | Master switch — all six categories at once |