/retry and /undo set session_entry.conversation_history which does not
exist on SessionEntry. The truncated history was never written to disk,
so the next message reload picked up the full unmodified transcript.
Added SessionStore.rewrite_transcript() that persists changes to both
the JSONL file and SQLite database, and updated both commands to use it.
/reset accessed self.session_store._sessions which does not exist on
SessionStore (the correct attribute is _entries). Also replaced the
hand-coded session key with _generate_session_key() to fix WhatsApp DM
sessions using the wrong key format.
Closes#210
b7f8a17c24