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/migrate.rs

@@ -219,7 +219,8 @@ async fn rename_manager_container(coord: &Arc<Coordinator>) {
     // Move rootfs if it exists (may be absent for ephemeral containers).
     let old_rootfs = std::path::PathBuf::from("/var/lib/nixos-containers/root");
     let new_rootfs = std::path::PathBuf::from("/var/lib/nixos-containers/h-root");
-    if old_rootfs.exists() && !new_rootfs.exists()
+    if old_rootfs.exists()
+        && !new_rootfs.exists()
         && let Err(e) = std::fs::rename(&old_rootfs, &new_rootfs)
     {
         tracing::warn!(error = ?e, "migration phase 5: rename rootfs failed (non-fatal)");