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/broker.rs

@@ -121,7 +121,11 @@ pub enum MessageEvent {
     /// `recv_blocking_batch` for the target agent but is not stored,
     /// not re-delivered on restart, and not shown in message history.
     /// Used for bash task completion notifications.
-    Ping { to: String, from: String, body: String },
+    Ping {
+        to: String,
+        from: String,
+        body: String,
+    },
 }
 
 /// Per-recipient in-memory bookkeeping for the deliver-then-ack
@@ -423,11 +427,7 @@ impl Broker {
                 // Transient ping — not sqlite-backed. Return it directly as
                 // a Delivery with id=0 (sentinel: never pushed to unacked_ids
                 // so ack_turn silently ignores it).
-                Ok(Ok(MessageEvent::Ping {
-                    to,
-                    from,
-                    body,
-                })) if to == recipient => {
+                Ok(Ok(MessageEvent::Ping { to, from, body })) if to == recipient => {
                     // Also drain any real sqlite messages that may have landed
                     // concurrently; prepend the ping so the agent sees both.
                     let mut batch = self.recv_batch(recipient, max.saturating_sub(1))?;