Terminal-started sessions can never be controlled from the dashboard
(hooks are one-way, no stdin channel into an externally-spawned
process) — tmux is the only mechanism that gives a second attached
client real two-way control. Replaces the stream-json/chat-bubble Run
feature entirely with a real tmux-backed PTY streamed via xterm.js,
while leaving hook-derived session/agent data (already synced
independent of the run mechanism) untouched.
