[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/Persistence/SaveData.cs

@@ -1,6 +1,9 @@
 using System;
 using System.Collections.Generic;
 
+namespace YachtDice.Persistence
+{
+
 [Serializable]
 public sealed class SaveData
 {
@@ -16,3 +19,4 @@ public sealed class ModifierSaveEntry
     public bool IsActive;
     public int RemainingUses;
 }
+}

Assets/Scripts/Persistence/SaveSystem.cs

@@ -1,6 +1,9 @@
 using Newtonsoft.Json;
 using UnityEngine;
 
+namespace YachtDice.Persistence
+{
+
 public static class SaveSystem
 {
     private const string SaveKey = "YachtDice_SaveData";
@@ -40,3 +43,4 @@ public static class SaveSystem
         return PlayerPrefs.HasKey(SaveKey);
     }
 }
+}