per-channel message logs with shared ChannelLog type

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>

src/thalamus/mod.rs

@@ -5,6 +5,7 @@
 // code (in claude/) and the future substrate-independent consciousness
 // binary.
 
+pub mod channel_log;
 pub mod channels;
 pub mod idle;
 pub mod supervisor;