refactor: oneshot agentd sessions per mention

Drop persistent sessions entirely. Each @slop mention is now a fresh
create → start → send → recv → stop cycle. No session state to go stale,
no restart logic, no binary-mismatch errors.

Conversation memory comes from Zulip topic history (already wired),
not agentd session state. DMs still work via unique per-message session names.

Removes: _sessions dict, _session_running(), _start_session(), _stop_session(),
         _reap_idle_sessions(), all stale-retry logic
Adds: _unique_session_name() (timestamp-suffixed), simplified ask_agentd()

0 files changed, 0 insertions, 0 deletions