[Refactor] Add folder-based namespaces to all C# scripts

Wrap all 39 scripts and 6 test files in namespaces matching their folder
structure (e.g. Assets/Scripts/Dice/ → YachtDice.Dice). Add cross-namespace
using directives where types are referenced across modules. Set rootNamespace
in both .asmdef files (YachtDice, YachtDice.Tests).

Namespace mapping:
- YachtDice.Dice — Dice, DiceRoller
- YachtDice.Economy — CurrencyBank
- YachtDice.Game — GameManager, DiceManager, DebugGameInput
- YachtDice.Inventory — InventoryController/Model/SlotView/View
- YachtDice.Modifiers — ModifierData/Effect/Enums/Pipeline/Runtime/Target
- YachtDice.Persistence — SaveData, SaveSystem
- YachtDice.Scoring — CategoryScorer, ScoreResult, ScoringSystem, YachtCategory
- YachtDice.Shop — ShopCatalog/Controller/ItemView/Model/View
- YachtDice.UI — CategoryRowView, DicePanelView, GameController, GameInfoView, ScoreCardView
- YachtDice.Editor — ModifierAssetCreator
- YachtDice.Tests — all test files

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

Assets/Scripts/Shop/ShopCatalog.cs

@@ -1,5 +1,9 @@
 using System.Collections.Generic;
 using UnityEngine;
+using YachtDice.Modifiers;
+
+namespace YachtDice.Shop
+{
 
 [CreateAssetMenu(fileName = "ShopCatalog", menuName = "YachtDice/Shop Catalog")]
 public sealed class ShopCatalog : ScriptableObject
@@ -18,3 +22,4 @@ public sealed class ShopCatalog : ScriptableObject
         return null;
     }
 }
+}