N5/D1c: the finale — !expedition start epilogue

Closes the Hollow King arc with a solo one-shot boss fight, reached via
`!expedition start epilogue` (intercepted before the zone/loadout
machinery). Unlock: all 24 journal pages found + both Tier-5 zones cleared.

- Encounter: runZoneCombat + renderBossOutcome, the arena's own pattern —
  no supplies, no walk, no party, no new mechanics. The stat block is
  Belaxath's (the abyss boss whose gate "lets one thing come home")
  re-dressed as the King returned in full, HP ×1.25 for a capstone; the
  ability/AC/CR carry over unchanged.
- Reward-once: first clear grants a unique title ("Kingsbane") + one
  Legendary + a games-room notice; later clears are a flavour-only
  rematch. The flag is a dedicated player_meta.epilogue_cleared column,
  latched by an atomic UPDATE (never the bulk save) so the monotonic
  false→true can't be clobbered — same discipline as D1a's journal
  bitmask. A loss costs a death, as any boss fight does.
- Title is written after a fresh character reload so runZoneCombat's
  post-fight HP persist isn't overwritten (the survivalist-milestone
  gotcha).

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

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

internal/plugin/dnd_expedition_cmd.go

@@ -283,6 +283,12 @@ func (p *AdventurePlugin) expeditionCmdStart(ctx MessageContext, c *DnDCharacter
 			formatRespecDuration(remaining)))
 	}
 	zoneTok, packTok := splitFirstWord(rest)
+	// N5/D1c: the campaign finale is reached here but is not a normal zone — it
+	// runs a single auto-resolved boss fight with its own unlock gate, no
+	// supplies, no walk. Intercept before the zone/loadout machinery.
+	if strings.EqualFold(zoneTok, "epilogue") {
+		return p.handleEpilogueEncounter(ctx)
+	}
 	available := zonesForLevel(c.Level)
 	zoneID, ok := resolveZoneInput(zoneTok, available)
 	if !ok {