N5/D1a: journal pages — the Hollow King campaign collectible

First slice of the N5 story layer. Adds a 24-page serialized campaign
threaded through the zones as collectible journal pages.

- Storage: one journal_pages INTEGER bitmask on player_meta (bit i ==
  page i+1). DEFAULT 0 is correct for every existing row, so no bootstrap.
  Grants are an atomic bitwise-OR (INSERT ... ON CONFLICT DO UPDATE SET
  journal_pages = journal_pages | excluded.journal_pages) so a page found
  mid-expedition can't be lost to a stale character save. Journal pages
  are therefore grant-only + overlay-read, never in the bulk upsert.
- Drop seam: elite kills roll a page (22%, tunable) in dropZoneLoot,
  gated on isElite — bosses get epilogues (D1b), not pages. Not on
  SimulateCombat's path, so TestCombatCharacterization is byte-identical.
- Viewer: !adventure journal renders found pages in story order with runs
  of missing pages collapsed to a single "…".
- Catalog + bitmask helpers + render live in the new
  adventure_flavor_campaign.go; the pages are in-world found artifacts,
  not TwinBee's voice.

Golden byte-identical; go test ./... green (incl. a real-DB round-trip
that pins the atomic OR + overlay read).

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

internal/plugin/dnd_zone_loot.go

@@ -517,6 +517,13 @@ func (p *AdventurePlugin) dropZoneLoot(userID id.UserID, zoneID ZoneID, monster
 			extra = append(extra, line)
 		}
 	}
+	// The Hollow King campaign (N5/D1). Elites carry the scattered pages; the
+	// gating boss gets an epilogue instead (D1b), not a page.
+	if isElite {
+		if line := p.maybeDropJournalPage(userID, nil); line != "" {
+			extra = append(extra, line)
+		}
+	}
 	trailer := strings.Join(extra, "\n")
 
 	entry, tier, ok := rollZoneLoot(zoneID, monster.CR, isBoss, nil)