mischief: tighten the detail page's live poll and drop dead state

The who-page poll now keeps the location line honest both ways (a mark
that came back to town stops showing its old expedition) and stops
polling once the adventurer leaves the board. Also collapses a redundant
branch in ResolveMischiefOrder and removes the always-false whoPage.Stale.

internal/web/who.go

@@ -54,7 +54,6 @@ var abilityLabels = [6]string{"STR", "DEX", "CON", "INT", "WIS", "CHA"}
 type whoPage struct {
 	pageData
 	Mark      RosterView
-	Stale     bool
 	HasDetail bool
 	Detail    whoDetail
 	Abilities []abilityRow
@@ -90,7 +89,6 @@ func (s *Server) handleAdventureWho(w http.ResponseWriter, r *http.Request) {
 	page := whoPage{
 		pageData: base,
 		Mark:     toRosterView(entry),
-		Stale:    storage.RosterSnapshotAt() == 0,
 	}
 	if d, abil, ok := decodeWhoDetail(entry.Detail); ok {
 		page.HasDetail = true