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.go

@@ -213,7 +213,7 @@ func (s *Server) handleAdventureWho(w http.ResponseWriter, r *http.Request) {
 		if page.MoreHistory {
 			events = events[:timelineCap]
 		}
-		page.Timeline = buildTimeline(s, events)
+		page.Timeline = buildTimeline(s, entry.Name, events)
 	}
 
 	// Owner enrichment: only when the signed-in user's localpart owns this exact
@@ -279,14 +279,14 @@ func (s *Server) handleAdventureWhoAPI(w http.ResponseWriter, r *http.Request) {
 // ever: Josie brings down the Rotmother"), and forty of those stacked in a column
 // read as a wall of shouting. The trail wants the noun, not the announcement. It
 // also saves a join back to stories for every row.
-func buildTimeline(s *Server, events []storage.AdvEvent) []timelineEntry {
+func buildTimeline(s *Server, subject string, events []storage.AdvEvent) []timelineEntry {
 	out := make([]timelineEntry, 0, len(events))
 	for _, e := range events {
 		label, emoji := advEventMeta(e.EventType)
 		out = append(out, timelineEntry{
 			Emoji:     emoji,
 			Label:     label,
-			Line:      timelineLine(e),
+			Line:      timelineLine(subject, e),
 			When:      time.Unix(e.OccurredAt, 0).UTC().Format("Jan 2, 2006"),
 			Permalink: s.advPermalink(e.GUID),
 			// A realm-first hoard is the treasure worth an eye; a plain find rides
@@ -301,7 +301,7 @@ func buildTimeline(s *Server, events []storage.AdvEvent) []timelineEntry {
 // timelineLine is the short "what" of a fact: the monster, the zone, the rival.
 // Empty is fine — the label and emoji already carry the event, and inventing
 // filler for a fact that carries no nouns would just be noise.
-func timelineLine(e storage.AdvEvent) string {
+func timelineLine(subject string, e storage.AdvEvent) string {
 	inZone := func(s string) string {
 		if e.Zone == "" {
 			return s
@@ -321,8 +321,16 @@ func timelineLine(e storage.AdvEvent) string {
 		}
 		return e.Zone
 	case "rival_result", "pete_duel_win", "pete_duel_loss":
-		if e.Opponent != "" {
-			return "vs " + e.Opponent
+		// Name the *other* party. On the winner's page the rival is the opponent;
+		// on the loser's page this fact arrives via the opponent column, so the
+		// rival is the subject — naming e.Opponent there would point the viewer at
+		// themselves. Pete duels carry no character opponent, so this stays empty.
+		other := e.Opponent
+		if e.Opponent == subject {
+			other = e.Subject
+		}
+		if other != "" && other != subject {
+			return "vs " + other
 		}
 		return ""
 	case "milestone":