adventure: fix three review findings on the who page

- timelineLine named the viewer as their own rival on a lost duel: a
  rival_result arrives on the loser's page via the opponent column, so
  naming the opponent field pointed at themselves. Thread the page
  character's name through and name the other party.
- buildMapView drew a frontier room twice when two visited rooms both
  had a door to it (Nodes carried the id twice). Place each id once.
- proseGuard's board query ran before the IsGUIDSeen dedup, so a retried
  dispatch paid for it and threw it away. Check dedup first.

internal/web/who_map.go

@@ -116,7 +116,16 @@ func buildMapView(m *whoMap) *mapView {
 	// Group nodes by depth column, each column ordered by first appearance.
 	maxDepth := 0
 	byCol := map[int][]string{}
+	placed := make(map[string]bool, len(m.Nodes))
 	for _, n := range m.Nodes {
+		// Two visited rooms can both list a door to the same withheld frontier
+		// room, so the same id can appear twice in Nodes. Place it once, or it
+		// draws as two overlapping discs and its edges resolve to whichever copy
+		// landed last.
+		if placed[n.ID] {
+			continue
+		}
+		placed[n.ID] = true
 		d := depth[n.ID]
 		byCol[d] = append(byCol[d], n.ID)
 		if d > maxDepth {