test(app): add headless ViewModel, CLI and localization tests

ViewModels run on Avalonia.Headless: wizard flows, password and file-lock
handling, seed and private-key reveal gating, contacts, settings, sync and
send against the fake server. The CLI entry point is invoked in-process
end to end. Localization checks cover the 7 languages, placeholders and
keys used in sources. Internal seams (UpdateCheck, ProfileOverride) keep
the tests offline.

tests/PalladiumWallet.Tests/App/LocalizationTests.cs

@@ -0,0 +1,88 @@
+using System.Reflection;
+using System.Text.RegularExpressions;
+using PalladiumWallet.App.Localization;
+
+namespace PalladiumWallet.Tests.App;
+
+/// <summary>
+/// Consistency of the in-code translation table: every key must have a non-empty value for
+/// each of the 7 languages, format placeholders must match across languages, and every key
+/// referenced from XAML or C# must exist (a missing key silently renders as the raw key).
+/// </summary>
+[Collection("AppPaths")] // shares the serialized collection for process-wide statics (Loc.Instance, AppPaths)
+public partial class LocalizationTests
+{
+    private static Dictionary<string, string[]> Table() =>
+        (Dictionary<string, string[]>)typeof(Loc)
+            .GetField("Strings", BindingFlags.NonPublic | BindingFlags.Static)!.GetValue(null)!;
+
+    [Fact]
+    public void EveryKey_HasOneNonEmptyValuePerLanguage()
+    {
+        var bad = Table()
+            .Where(kv => kv.Value.Length != Loc.Languages.Length || kv.Value.Any(string.IsNullOrWhiteSpace))
+            .Select(kv => kv.Key).ToList();
+        Assert.True(bad.Count == 0, "Incomplete translations: " + string.Join(", ", bad));
+    }
+
+    [Fact]
+    public void LanguageNames_MatchLanguages() =>
+        Assert.Equal(Loc.Languages.Length, Loc.LanguageNames.Length);
+
+    [Fact]
+    public void FormatPlaceholders_AreIdenticalAcrossLanguages()
+    {
+        var bad = new List<string>();
+        foreach (var (key, values) in Table())
+        {
+            var sets = values.Select(v => string.Join(",", Placeholder().Matches(v).Select(m => m.Value).Distinct().Order())).ToList();
+            if (sets.Distinct().Count() > 1) bad.Add($"{key}: {string.Join(" | ", sets)}");
+        }
+        Assert.True(bad.Count == 0, "Placeholder mismatch: " + string.Join("; ", bad));
+    }
+
+    [Fact]
+    public void Indexer_ReturnsTranslationPerLanguage_AndFallsBackToKey()
+    {
+        try
+        {
+            var table = Table();
+            var key = table.Keys.First();
+            for (var i = 0; i < Loc.Languages.Length; i++)
+                Assert.Equal(table[key][i], Loc.SwitchTo(Loc.Languages[i])[key]);
+            Assert.Equal("no.such.key", Loc.Tr("no.such.key"));
+            Assert.Equal("en", Loc.SwitchTo("xx").Language); // unknown language → English
+        }
+        finally { Loc.SwitchTo("en"); }
+    }
+
+    [Fact]
+    public void KeysUsedInSources_ExistInTable()
+    {
+        var root = RepoRoot();
+        if (root is null) return; // running from a packaged copy without sources
+        var keys = Table().Keys.ToHashSet();
+        var missing = new SortedSet<string>();
+        foreach (var file in Directory.EnumerateFiles(Path.Combine(root, "src", "App"), "*.*", SearchOption.AllDirectories)
+                     .Where(f => (f.EndsWith(".axaml") || f.EndsWith(".cs")) && !f.Contains($"{Path.DirectorySeparatorChar}obj{Path.DirectorySeparatorChar}")
+                                 && !f.Contains($"{Path.DirectorySeparatorChar}bin{Path.DirectorySeparatorChar}")
+                                 && Path.GetFileName(f) != "Loc.cs")) // Loc.cs only mentions the syntax in comments
+        {
+            var text = File.ReadAllText(file);
+            foreach (Match m in XamlKey().Matches(text)) if (!keys.Contains(m.Groups[1].Value)) missing.Add(m.Groups[1].Value);
+            foreach (Match m in CodeKey().Matches(text)) if (!keys.Contains(m.Groups[1].Value)) missing.Add(m.Groups[1].Value);
+        }
+        Assert.True(missing.Count == 0, "Keys used but not defined: " + string.Join(", ", missing));
+    }
+
+    private static string? RepoRoot()
+    {
+        for (var d = new DirectoryInfo(AppContext.BaseDirectory); d is not null; d = d.Parent)
+            if (File.Exists(Path.Combine(d.FullName, "PalladiumWallet.sln"))) return d.FullName;
+        return null;
+    }
+
+    [GeneratedRegex(@"\{\d+(?::[^}]*)?\}")] private static partial Regex Placeholder();
+    [GeneratedRegex(@"Loc\[([A-Za-z0-9_.]+)\]")] private static partial Regex XamlKey();
+    [GeneratedRegex(@"Loc\.Tr\(""([A-Za-z0-9_.]+)""\)")] private static partial Regex CodeKey();
+}