fix(levels): ScenePath must be a string, not a PackedScene

slice 7 regression. level_village_2..5.tscn each reference their own
LevelResource for the death screen label, so pointing the resource back
at the scene forms a cycle Godot cannot resolve - "Parse Error: Busy"
and the level fails to load entirely.

ScenePath was a string for exactly this reason. Reverted, and the rot it
allowed (forest_1 aimed at a nonexistent scene) is now caught by
LevelCatalogue.Validate checking every path resolves, plus a repo-level
structural check - fixed by validation rather than by typing.

project.godot: restores the C# feature flag and dialogue_manager
uses_dotnet, which `godot --headless --import` strips on every run.

scripts/Resources/LevelCatalogue.cs

@@ -27,8 +27,8 @@ public partial class LevelCatalogue : Resource
 
     /// <summary>
     /// The ordering the domain works from. Throws if the authored data is inconsistent — a blank or
-    /// duplicated id cannot produce a <see cref="Campaign"/>, so a mistake here fails at boot rather
-    /// than corrupting a save later.
+    /// duplicated id cannot produce a <see cref="Campaign"/>, so a mistake fails at boot rather than
+    /// corrupting a save later.
     /// </summary>
     public Campaign ToCampaign()
     {
@@ -36,19 +36,48 @@ public partial class LevelCatalogue : Resource
 
         for (var i = 0; i < Levels.Count; i++)
         {
-            var level = Levels[i];
-            if (level == null)
-                throw new System.InvalidOperationException(
-                    $"LevelCatalogue has an empty slot at index {i}.");
+            if (Levels[i] == null)
+                throw new System.InvalidOperationException($"LevelCatalogue has an empty slot at index {i}.");
 
-            ids.Add(LevelId.Of(level.Id));
+            ids.Add(LevelId.Of(Levels[i].Id));
         }
 
         return Campaign.Of(ids);
     }
 
+    /// <summary>
+    /// Checks every catalogued Level names a scene that actually exists, returning the problems found.
+    /// </summary>
+    /// <remarks>
+    /// This is what keeps <see cref="LevelResource.ScenePath"/> honest. The path cannot be a typed
+    /// <c>PackedScene</c> — several level scenes reference their own LevelResource, so a reference back
+    /// to the scene is a cycle Godot reports as "Parse Error: Busy" and the level fails to load. A
+    /// string plus this check gets the safety without the cycle.
+    /// </remarks>
+    public IReadOnlyList<string> Validate()
+    {
+        var problems = new List<string>();
+
+        foreach (var level in Levels.Where(l => l != null))
+        {
+            if (string.IsNullOrWhiteSpace(level.ScenePath))
+                problems.Add($"level '{level.Id}' has no scene path");
+            else if (!ResourceLoader.Exists(level.ScenePath))
+                problems.Add($"level '{level.Id}' points at '{level.ScenePath}', which does not exist");
+        }
+
+        return problems;
+    }
+
     public LevelResource Find(LevelId id) =>
         Levels.FirstOrDefault(level => level != null && level.Id == id.Value);
 
-    public PackedScene SceneFor(LevelId id) => Find(id)?.Scene;
+    /// <summary>Loads a Level's scene on demand. Null when the Level is not catalogued.</summary>
+    public PackedScene SceneFor(LevelId id)
+    {
+        var path = Find(id)?.ScenePath;
+        return string.IsNullOrWhiteSpace(path) ? null : ResourceLoader.Load<PackedScene>(path);
+    }
+
+    public string DisplayNameKeyFor(LevelId id) => Find(id)?.LevelName ?? string.Empty;
 }