feat(#1137): rich unread summary in loose ends and wake signal

- hive-sh4re: UnreadMatrix gains summary: String field (per-room breakdown)
- hive-matrix-mcp/protocol: add RoomUnread struct + UnreadSummary request
- hive-matrix-mcp/handlers: collect_unread() fetches per-room data;
  single-unread rooms include truncated last-message body + sender;
  multi-unread rooms carry count only
- hive-matrix-mcp/wake: format_unread_summary() builds wake body from
  RoomUnread slice; terse one-liner for single-room/single-message,
  bulleted list for multi-room; always appends read-hint
- hive-matrix-mcp/timeline: wake body now covers all rooms with unread
  at fire time, not just the triggering event; falls back to per-event
  teaser if notification counts haven't updated yet
- hive-ag3nt/mcp: matrix_unread_summary() replaces matrix_unread_rooms();
  UnreadMatrix loose end carries per-room summary lines; render shows
  room breakdown with sender: body for single-unread rooms

hive-c0re/src/rebuild_queue.rs

@@ -277,7 +277,16 @@ impl RebuildQueue {
         reason: String,
         parent_id: Option<u64>,
     ) -> u64 {
-        self.enqueue_full(kind, agent, source, reason, parent_id, Vec::new(), None, None)
+        self.enqueue_full(
+            kind,
+            agent,
+            source,
+            reason,
+            parent_id,
+            Vec::new(),
+            None,
+            None,
+        )
     }
 
     /// Same as `enqueue` but carries an `inputs` payload — used by
@@ -1304,14 +1313,20 @@ mod tests {
             Some(meta),
         );
         // The two Rebuilds have different parent_ids — must NOT dedup.
-        assert_ne!(sweep_rebuild, cascade_rebuild,
-            "cascade rebuild must be distinct from startup-sweep rebuild");
+        assert_ne!(
+            sweep_rebuild, cascade_rebuild,
+            "cascade rebuild must be distinct from startup-sweep rebuild"
+        );
         let snap = q.snapshot();
-        let rebuilds: Vec<_> = snap.iter()
+        let rebuilds: Vec<_> = snap
+            .iter()
             .filter(|e| e.kind == QueueKind::Rebuild && e.agent == "alice")
             .collect();
-        assert_eq!(rebuilds.len(), 2,
-            "both rebuilds must be present in the queue");
+        assert_eq!(
+            rebuilds.len(),
+            2,
+            "both rebuilds must be present in the queue"
+        );
     }
 
     #[test]