feat(federation): enhance bd federation status command (bd-wkumz.5)

Improve the federation status command to show more comprehensive
information similar to `git remote -v` with health info:

- Show peer URLs alongside peer names
- Display pending local changes count (uncommitted)
- Test connectivity to each peer (via fetch)
- Track and display last sync time in metadata table
- Show reachability status with error messages on failure

Changes:
- cmd/bd/federation.go: Enhanced status output with URLs, connectivity
  checks, pending changes, and last sync time
- internal/storage/dolt/federation.go: Added getLastSyncTime/setLastSyncTime
  methods using metadata table, record sync time on successful sync

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

internal/storage/dolt/federation.go

@@ -118,12 +118,36 @@ func (s *DoltStore) SyncStatus(ctx context.Context, peer string) (*storage.SyncS
 		status.HasConflicts = true
 	}
 
-	// TODO: Track last sync time in metadata
-	status.LastSync = time.Time{} // Zero time indicates never synced
+	// Get last sync time from metadata
+	status.LastSync = s.getLastSyncTime(ctx, peer)
 
 	return status, nil
 }
 
+// getLastSyncTime retrieves the last sync time for a peer from metadata.
+func (s *DoltStore) getLastSyncTime(ctx context.Context, peer string) time.Time {
+	key := "last_sync_" + peer
+	var value string
+	err := s.db.QueryRowContext(ctx, "SELECT value FROM metadata WHERE `key` = ?", key).Scan(&value)
+	if err != nil {
+		return time.Time{}
+	}
+	t, err := time.Parse(time.RFC3339, value)
+	if err != nil {
+		return time.Time{}
+	}
+	return t
+}
+
+// setLastSyncTime records the last sync time for a peer in metadata.
+func (s *DoltStore) setLastSyncTime(ctx context.Context, peer string) error {
+	key := "last_sync_" + peer
+	value := time.Now().Format(time.RFC3339)
+	_, err := s.db.ExecContext(ctx,
+		"REPLACE INTO metadata (`key`, value) VALUES (?, ?)", key, value)
+	return err
+}
+
 // Sync performs a full bidirectional sync with a peer:
 // 1. Fetch from peer
 // 2. Merge peer's changes (handling conflicts per strategy)
@@ -195,6 +219,9 @@ func (s *DoltStore) Sync(ctx context.Context, peer string, strategy string) (*Sy
 		result.Pushed = true
 	}
 
+	// Record last sync time
+	_ = s.setLastSyncTime(ctx, peer)
+
 	result.EndTime = time.Now()
 	return result, nil
 }