Add multi-base resource group support to the TUI editor

The Terminal.Gui editor assumed a flat single-group model: it crashed on
startup with a multi-group directory (duplicate DataTable column names),
showed only the first group's keys, and silently wrote edits to the wrong
group's file.

- Data model: entries are tracked per group (EntryReference.BaseName); the
  table builds one column per distinct culture code plus a Group column, and
  loads keys from every group's default file. Hidden _BaseName column makes
  row->entry mapping group-aware.
- Operations are scoped to a key's group: edit, plural edit, add, delete,
  merge, translate, copy/paste and add/remove language all resolve target
  files by (BaseName, Code) instead of by Code alone. Add Language creates a
  file for every group; Remove Language removes a culture across all groups.
- Default-language labels use IsDefault and the configured default code
  (e.g. "it (Default)") instead of assuming an empty code, matching this
  session's core fix.
- Extra-key and duplicate detection run per group.

Adds headless FakeDriver smoke tests covering multi-group and single-group
construction (the previously-crashing path).

Author: nickprotop

LocalizationManager.Tests/IntegrationTests/TuiMultiGroupSmokeTests.cs

@@ -0,0 +1,102 @@
+// Copyright (c) 2025 Nikolaos Protopapas
+// Licensed under the MIT License
+
+using LocalizationManager.Core.Backends.Resx;
+using LocalizationManager.Core.Models;
+using LocalizationManager.UI;
+using Terminal.Gui;
+using Xunit;
+
+namespace LocalizationManager.Tests.IntegrationTests;
+
+/// <summary>
+/// Smoke tests for the TUI editor against multi-base resource group directories.
+/// Before multi-group support, constructing the editor with two groups that share a
+/// culture code crashed (duplicate DataTable column names). These tests build a real
+/// multi-group directory and confirm the window constructs without throwing.
+/// </summary>
+[Collection("Tui")]
+public class TuiMultiGroupSmokeTests : IDisposable
+{
+    private readonly string _tempDir;
+    private readonly ResxResourceDiscovery _discovery = new("it");
+    private readonly ResxResourceReader _reader = new();
+
+    public TuiMultiGroupSmokeTests()
+    {
+        _tempDir = Path.Combine(Path.GetTempPath(), $"TuiMultiGroup_{Guid.NewGuid()}");
+        Directory.CreateDirectory(_tempDir);
+    }
+
+    public void Dispose()
+    {
+        try { Application.Shutdown(); } catch { /* not initialized */ }
+        if (Directory.Exists(_tempDir)) Directory.Delete(_tempDir, true);
+    }
+
+    private void WriteResx(string fileName, params (string Key, string Value)[] entries)
+    {
+        var body = string.Join("\n", entries.Select(e =>
+            $"  <data name=\"{e.Key}\" xml:space=\"preserve\"><value>{e.Value}</value></data>"));
+        var content =
+            "<?xml version=\"1.0\" encoding=\"utf-8\"?>\n<root>\n" +
+            "  <resheader name=\"resmimetype\"><value>text/microsoft-resx</value></resheader>\n" +
+            "  <resheader name=\"version\"><value>2.0</value></resheader>\n" +
+            "  <resheader name=\"reader\"><value>System.Resources.ResXResourceReader</value></resheader>\n" +
+            "  <resheader name=\"writer\"><value>System.Resources.ResXResourceWriter</value></resheader>\n" +
+            body + "\n</root>\n";
+        File.WriteAllText(Path.Combine(_tempDir, fileName), content);
+    }
+
+    private List<ResourceFile> DiscoverAndRead()
+    {
+        var languages = _discovery.DiscoverLanguages(_tempDir);
+        return languages.Select(l => _reader.Read(l)).ToList();
+    }
+
+    [Fact]
+    public void Constructor_MultipleGroupsSharingCulture_DoesNotThrow()
+    {
+        // Two groups, each with a default + Italian file → same culture code "it" appears twice.
+        WriteResx("CustomerResources.resx", ("Customer_Name", "Name"));
+        WriteResx("CustomerResources.it.resx", ("Customer_Name", "Nome"));
+        WriteResx("GlassResources.resx", ("Glass_Width", "Width"));
+        WriteResx("GlassResources.it.resx", ("Glass_Width", "Larghezza"));
+
+        var resourceFiles = DiscoverAndRead();
+        var backend = new ResxResourceBackend("it");
+
+        Application.Init(new FakeDriver());
+        try
+        {
+            // The window construction is what used to crash with a DuplicateNameException.
+            var window = new ResourceEditorWindow(resourceFiles, backend, "it", _tempDir);
+            Assert.NotNull(window);
+        }
+        finally
+        {
+            Application.Shutdown();
+        }
+    }
+
+    [Fact]
+    public void Constructor_SingleGroup_DoesNotThrow()
+    {
+        WriteResx("Resources.resx", ("Hello", "Hello"));
+        WriteResx("Resources.it.resx", ("Hello", "Ciao"));
+
+        var resourceFiles = DiscoverAndRead();
+        var backend = new ResxResourceBackend("it");
+
+        Application.Init(new FakeDriver());
+        try
+        {
+            var window = new ResourceEditorWindow(resourceFiles, backend, "it", _tempDir);
+            Assert.NotNull(window);
+        }
+        finally
+        {
+            Application.Shutdown();
+        }
+    }
+}

UI/ResourceEditorWindow/ResourceEditorWindow.BatchOperations.cs

@@ -254,7 +254,7 @@ private void BulkDelete()
                 // Delete each selected entry
                 foreach (var entryRef in selectedEntries)
                 {
-                    DeleteSpecificOccurrence(entryRef.Key, entryRef.OccurrenceNumber);
+                    DeleteSpecificOccurrence(entryRef.Key, entryRef.OccurrenceNumber, entryRef.BaseName);
                 }
 
                 _hasUnsavedChanges = true;