feat(c5): prune old tmux logs and share pipe-pane helper

Extract the tmux pipe-pane setup into functions/_tmux_pipe_log.fish,
called by both conf.d/tmux-logging.fish (startup) and
__fish_config_sync_logging (C5 re-enable). The helper prunes the oldest
tmux_*.log files by mtime to stay within SCROLLBACK_HISTORY_MAX_FILES,
matching the paru/yay wrappers.

Uses 'command ls' to bypass the eza ls shadow, which injects OSC-8
hyperlink escapes into paths and corrupted the filenames passed to rm.

functions/__fish_config_sync_logging.fish

@@ -34,14 +34,7 @@ function __fish_config_sync_logging --description 'Sync C5 logging state: sentin
         rm -f $sentinel
 
         # Restart tmux pipe-pane for the current pane if inside tmux
-        if set -q TMUX
-            set -l log_dir (set -q SCROLLBACK_HISTORY_DIR; and echo $SCROLLBACK_HISTORY_DIR; or echo "$HOME/.terminal_history")
-            set -l pane_id (tmux display-message -p '#{session_name}-w#{window_index}-p#{pane_index}' 2>/dev/null)
-            set -l timestamp (date "+%Y-%m-%d_%H-%M-%S")
-            set -l log_file "$log_dir/tmux_"$pane_id"_"$timestamp".log"
-            mkdir -p $log_dir
-            tmux pipe-pane "cat >> $log_file" 2>/dev/null
-        end
+        _tmux_pipe_log
 
         if test -x /usr/bin/paru
             mkdir -p (dirname $paru_wrapper)