adventure: show the party, the pets, and what you missed

Four small surfaces the game has had all along and the web has never shown.

The party roster on the adventurer page is the one with a bug behind it. The
board resolved an expedition by owner id, so a player seated on somebody else's
run has been reading as "idle in town" while standing in a tier-4 dungeon.
Seats now ride the roster detail beside the supply and threat numbers, and an
opted-out player's seat is anonymised rather than dropped: a party of three
rendered as a pair contradicts everything printed next to it.

Pets show their levelling. They have earned XP from every won fight since that
wiring was fixed and the only place a level ever appeared was a Matrix line
that scrolled away. The threshold comes from the engine, in the engine's own
centi-XP, because a copy of the curve here would drift the first time a band
moved.

"While you were away" is the one panel on the site about the reader rather than
the realm. Two stamps behind it, not one: a single column would show the news,
move the clock, and render an empty box over the same events on the reader's
first refresh.

And the story permalink names its region, which has been hardcoded empty behind
a `// reserved` comment since the page shipped.

internal/web/handlers.go

@@ -175,6 +175,11 @@ type channelPage struct {
 	// even with nothing camped, because the link to the history is the other half
 	// of what makes a live Siege feel like it counts.
 	Siege SiegeView
+
+	// Away is the signed-in owner's "while you were away" panel: what happened to
+	// their own adventurer since their last visit. Zero for everyone else, and
+	// zero for an owner who has missed nothing — see awayPanel.
+	Away awayView
 }
 
 type indexPage struct {
@@ -404,6 +409,7 @@ func (s *Server) handleChannel(w http.ResponseWriter, r *http.Request, ch Channe
 		data.Roster, data.RosterStale, _ = s.roster()
 		data.ShowRoster = true
 		data.Siege = s.siege()
+		data.Away = s.awayPanel(r)
 	}
 	s.render(w, "channel", data)
 }