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/Tests/Editor/SaveSystemTests.cs

@@ -89,5 +89,22 @@ namespace YachtDice.Tests
             Assert.IsNotNull(loaded);
             Assert.AreEqual(0, loaded.Currency);
         }
+
+        [Test]
+        public void SaveAndLoad_RoundTrip_PreservesDiceIds()
+        {
+            var data = new SaveData
+            {
+                Currency = 100,
+                OwnedDiceIds = new List<string> { "standard_d6", "chaos_d6" }
+            };
+
+            SaveSystem.Save(data);
+            var loaded = SaveSystem.Load();
+
+            Assert.AreEqual(2, loaded.OwnedDiceIds.Count);
+            Assert.AreEqual("standard_d6", loaded.OwnedDiceIds[0]);
+            Assert.AreEqual("chaos_d6", loaded.OwnedDiceIds[1]);
+        }
     }
 }