fix(cli): enable file watch for external sessions to ensure buffer re…

[hamidi-dev]

…load

Description

Fixes buffer auto-reload when using CLI tools (OpenCode, Aider, etc.) in window/split modes with external multiplexer sessions (tmux/zellij) Previously, file watching was only enabled for terminal sessions, causing buffers to remain stale after external edits.

Fix: Moved watch enablement to session/init.lua:attach() so it applies to all session types regardless of backend.