Rework shop to support multiple item types and add unified PlayerModel

Generalize the shop from selling only ModifierDefinition to any IShopItem
(modifiers + dice). Add purchase condition checks, hover tooltips, and
fixed prices. Introduce PlayerModel as a facade over CurrencyBank,
InventoryModel, and DiceCollection for centralized state and save/load.

New files:
- IShopItem interface for purchasable items
- ShopCatalog SO (unified catalog for all item types)
- ShopTooltipView (description on hover)
- PlayerModel (aggregates player state)
- DiceCollection (owned dice tracking)
- DiceCatalog SO (dice definition registry)
- DiceCollectionTests

Modified:
- ModifierDefinition/DieDefinitionSO implement IShopItem
- ShopModel/ShopView/ShopItemView/ShopController use IShopItem
- SaveData v3 with OwnedDiceIds
- GameController uses PlayerModel for save/load
- GameLifetimeScope registers new services

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Assets/Scripts/Modifiers/Definition/ModifierDefinition.cs

@@ -1,11 +1,12 @@
 using System.Collections.Generic;
 using UnityEngine;
 using YachtDice.Modifiers.Core;
+using YachtDice.Shop;
 
 namespace YachtDice.Modifiers.Definition
 {
     [CreateAssetMenu(fileName = "NewModifier", menuName = "YachtDice/Modifiers/Definition")]
-    public class ModifierDefinition : ScriptableObject
+    public class ModifierDefinition : ScriptableObject, IShopItem
     {
         [Header("Identity")]
         [SerializeField] private string id;
@@ -36,6 +37,7 @@ namespace YachtDice.Modifiers.Definition
         public bool HasLimitedUses => hasLimitedUses;
         public int MaxUses => maxUses;
         public int MaxStacks => maxStacks;
+        public bool IsRepurchasable => hasLimitedUses;
         public IReadOnlyList<ModifierBehavior> Behaviors => behaviors;
 
 #if UNITY_EDITOR