Pete Adventure News: emit seam, !news command, cold-start backfill

gogobee's game-side of Pete's push-based Adventure news feed. Emits
structured event *facts* (not prose) to Pete's ingest endpoint over a
durable queue; Pete owns voice/authoring/publishing.

- internal/peteclient: durable pete_emit_queue + retry sender; Fact
  payload; FEATURE_PETE_NEWS master switch.
- pete.go: emitFact enforces runtime kill-switch + per-player opt-out
  (anonymize, never drop); zone-clear + realm-first tiering; !news
  command (player optout/optin, admin on/off).
- bootstrap_pete_news.go: cold-start backfill replays deaths +
  single-holder achievements + zone realm-firsts, backdated + NoPush,
  idempotent, fires only once the seam is live; seeds news_realm_firsts.
- Emit sites: death, zone_first, rival_result, milestone, arrival.
- db.go: pete_emit_queue, news_optout (+opted_out_at), news_realm_firsts.

Unshipped. Deploy Pete first, then set FEATURE_PETE_NEWS + ingest env.

Claude-Session: https://claude.ai/code/session_017mEwUmmS7aQTP2NQXj6rUa

internal/plugin/adventure_duel.go

@@ -32,6 +32,7 @@ import (
 	"time"
 
 	"gogobee/internal/db"
+	"gogobee/internal/peteclient"
 
 	"github.com/google/uuid"
 	"maunium.net/go/mautrix/id"
@@ -613,6 +614,21 @@ func (p *AdventurePlugin) settleDuel(ctx MessageContext, ch *advDuelChallenge, c
 	upsertRivalRecord(winnerID, loserID, true)
 	upsertRivalRecord(loserID, winnerID, false)
 
+	// One BULLETIN dispatch per settled duel (from the winner's side, so it
+	// fires once). Character names only; no-op unless the seam is enabled.
+	if wn, ln := charName(winnerID), charName(loserID); wn != "" && ln != "" {
+		ts := nowUnix()
+		emitFact(peteclient.Fact{
+			GUID:       fmt.Sprintf("rival:%s:%s:%d", userHash(winnerID), userHash(loserID), ts),
+			EventType:  "rival_result",
+			Tier:       "bulletin",
+			Subject:    wn,
+			Opponent:   ln,
+			Outcome:    "won",
+			OccurredAt: ts,
+		}, winnerID, loserID)
+	}
+
 	p.announceDuel(ctx, winnerID, loserID, ch.Stake, winnerShare, potShare, res.decisive)
 	return nil
 }