N5/D1b: boss epilogues + TwinBee's journal reactions

- Boss epilogues: a 2-3 sentence campaign capstone per zone boss, tying
  each kill to the Hollow King arc. Appended to the boss-down moment in
  both close-out paths (finishCombatSession solo, finishPartyWin party),
  gated on the boss room (!elite) so it fires for any boss kill —
  expedition or legacy !zone — and never for elites or the arena (which
  has no ZoneID entry). Forest of Shadows is the King himself; its
  epilogue frames the fall as a shed shell, leaving the arc for the finale.
- TwinBee digest reactions: a journal page found mid-expedition writes a
  "journal" log beat; the end-of-day digest emits one first-person,
  deterministically-picked TwinBee line reacting to the day's pages. No
  net-new DM — it rides the existing night-camp digest.

Golden byte-identical; go test ./... green.

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

internal/plugin/combat_cmd.go

@@ -381,6 +381,11 @@ func (p *AdventurePlugin) finishCombatSession(userID id.UserID, sess *CombatSess
 		if drop := p.dropZoneLoot(userID, zone.ID, monster, !elite, elite); drop != "" {
 			b.WriteString(drop + "\n")
 		}
+		if !elite {
+			if ep := bossEpilogueLine(zone.ID); ep != "" {
+				b.WriteString("\n" + ep + "\n")
+			}
+		}
 		if bossOnExpedition {
 			// The boss is the expedition's climax. Frame the close-out as
 			// the win rather than a "keep walking" nudge. One more