Move ChannelLog to src/thalamus/channel_log.rs — shared by all
channel daemon implementations. Each channel/PM gets its own
log with consumed/unread tracking.
IRC daemon: channels tracked via BTreeMap<String, ChannelLog>.
list() returns all channels (joined + PMs) with per-channel
unread counts. Sent messages stored in logs too.
Co-Developed-By: Kent Overstreet <kent.overstreet@linux.dev>
