D&D: wire the Open5e magic-item registry into live gameplay

Magic items now reach players through three surfaces: zone loot drops,
Luigi's "Curios" shelf, and combat effects. Effects are formulaic
(Rarity scalar x Kind), mirroring the bestiary tuning pass, with an
empty magicItemEffectOverlay as the hand-authored refinement path.

- magic_items_gameplay.go: rarity index, magic_item_equipped persistence
  (new table, DnDSlot-keyed), codified effect formula, applyMagicItemEffects
  combat hook, potion/scroll -> ConsumableDef bridge, !adventure equip-magic
- dropZoneLoot: 15% magic-item substitution roll by tier rarity
- Luigi's Curios category: daily UTC-seeded 8-item rotation
- combat_bridge / combat_session_build: applyMagicItemEffects after passives
- consumableDefByName falls through so loot/shop potions auto-resolve
- renderDnDSheet: new Magic Items section

Equippable items live entirely in the DnDSlot scheme, separate from the
legacy tier-gear. Attunement items equip inert until attuned (3-slot cap).

internal/plugin/adventure_consumables.go

@@ -65,14 +65,17 @@ var consumableDefs = []ConsumableDef{
 	{Name: "Voidstone Shard", Effect: EffectReflect, Value: 0.50, Tier: 5, Buyable: false, Slot: "defensive"},
 }
 
-// consumableDefByName returns the definition for a consumable by name.
+// consumableDefByName returns the definition for a consumable by name. Falls
+// through to the magic-item registry so SRD potions/scrolls picked up as loot
+// or bought from Luigi's Curios shelf resolve in combat without being added
+// to the hardcoded consumableDefs table (see magic_items_gameplay.go).
 func consumableDefByName(name string) *ConsumableDef {
 	for i := range consumableDefs {
 		if consumableDefs[i].Name == name {
 			return &consumableDefs[i]
 		}
 	}
-	return nil
+	return magicItemConsumableDefByName(name)
 }
 
 // ── Threat Assessment ────────────────────────────────────────────────────────