Add OWML mod skeleton and import English translation template

Phase 2 (mod skeleton) + Phase 3 (import English source):

- manifest.json / SlovakTranslation.cs / ILocalizationAPI.cs registering
  "Slovenčina" via xen.LocalizationUtility (Interplanetary Polyglot).
- SlovakTranslation.csproj / .sln building net48 against the OWML and
  OuterWildsGameLibs NuGet packages — no game install needed to compile.
- assets/Translation.xml: English source template (896 KB, 2424 entries,
  keys == values) to be translated into Slovak.
- Project docs (README/PLAN/CLAUDE) and .gitignore.

Build verified: dotnet build -c Release stages a loadable mod folder.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

SlovakTranslation.cs

@@ -0,0 +1,35 @@
+using OWML.Common;
+using OWML.ModHelper;
+
+namespace SlovakTranslation
+{
+    /// <summary>
+    /// Registers Slovenčina as a selectable language via xen-42's Localization
+    /// Utility (xen.LocalizationUtility). All the heavy lifting lives in the
+    /// utility; this mod just points it at our translated strings.
+    /// </summary>
+    public class SlovakTranslation : ModBehaviour
+    {
+        public static SlovakTranslation Instance;
+
+        /// <summary>Path (relative to the mod folder) to the translated strings.</summary>
+        public static string translationFile = "assets/Translation.xml";
+
+        private void Start()
+        {
+            Instance = this;
+
+            var api = ModHelper.Interaction.TryGetModApi<ILocalizationAPI>("xen.LocalizationUtility");
+            if (api == null)
+            {
+                ModHelper.Console.WriteLine(
+                    "Could not find xen.LocalizationUtility — is Interplanetary Polyglot installed?",
+                    MessageType.Error);
+                return;
+            }
+
+            api.RegisterLanguage(this, "Slovenčina", translationFile);
+            ModHelper.Console.WriteLine("Registered language: Slovenčina", MessageType.Success);
+        }
+    }
+}