[GUI] Per-game launch settings + shared SettingRow (#2) (#378)

Add per-game launch overrides (log level, import-trace limit, strict dynlib
resolution, log-to-file, and SHARPEMU_* environment toggles) with three-tier
resolution (per-game override -> global preference -> built-in default), stored
one file per game at user/custom_configs/<titleId>.json. Editable from a new
"Game settings..." context-menu dialog.

Introduce a shared SettingRow control and adopt it across the Options page and
the per-game dialog so the two read as one app. Fully localized (reusing the
existing Options.* keys), with the actions pinned in the dialog footer.

src/SharpEmu.GUI/PerGameSettings.cs

@@ -0,0 +1,115 @@
+// Copyright (C) 2026 SharpEmu Emulator Project
+// SPDX-License-Identifier: GPL-2.0-or-later
+
+using System.Text.Json;
+using System.Text.Json.Serialization;
+
+namespace SharpEmu.GUI;
+
+public sealed class PerGameSettings
+{
+    private static readonly JsonSerializerOptions SerializerOptions = new()
+    {
+        WriteIndented = true,
+    };
+
+    public string? LogLevel { get; set; }
+
+    public int? ImportTraceLimit { get; set; }
+
+    public bool? StrictDynlibResolution { get; set; }
+
+    public bool? LogToFile { get; set; }
+
+    public List<string>? EnvironmentToggles { get; set; }
+
+    [JsonIgnore]
+    public bool IsEmpty =>
+        LogLevel is null &&
+        ImportTraceLimit is null &&
+        StrictDynlibResolution is null &&
+        LogToFile is null &&
+        EnvironmentToggles is null;
+
+    public static string DirectoryPath =>
+        Path.Combine(AppContext.BaseDirectory, "user", "custom_configs");
+
+    public static string PathFor(string titleId) =>
+        Path.Combine(DirectoryPath, SanitizeTitleId(titleId) + ".json");
+
+    public static PerGameSettings? Load(string? titleId)
+    {
+        if (string.IsNullOrWhiteSpace(titleId))
+        {
+            return null;
+        }
+
+        try
+        {
+            var path = PathFor(titleId);
+            if (File.Exists(path))
+            {
+                return JsonSerializer.Deserialize<PerGameSettings>(File.ReadAllText(path), SerializerOptions);
+            }
+        }
+        catch (Exception)
+        {
+        }
+
+        return null;
+    }
+
+    public void Save(string titleId)
+    {
+        if (string.IsNullOrWhiteSpace(titleId))
+        {
+            return;
+        }
+
+        try
+        {
+            var path = PathFor(titleId);
+            if (IsEmpty)
+            {
+                if (File.Exists(path))
+                {
+                    File.Delete(path);
+                }
+
+                return;
+            }
+
+            Directory.CreateDirectory(DirectoryPath);
+            File.WriteAllText(path, JsonSerializer.Serialize(this, SerializerOptions));
+        }
+        catch (Exception)
+        {
+        }
+    }
+
+    private static string SanitizeTitleId(string titleId)
+    {
+        var trimmed = titleId.Trim();
+        foreach (var invalid in Path.GetInvalidFileNameChars())
+        {
+            trimmed = trimmed.Replace(invalid, '_');
+        }
+
+        return trimmed.Length == 0 ? "UNKNOWN" : trimmed;
+    }
+}
+
+public sealed record EffectiveLaunchSettings(
+    string LogLevel,
+    int ImportTraceLimit,
+    bool StrictDynlibResolution,
+    bool LogToFile,
+    IReadOnlyList<string> EnvironmentToggles)
+{
+    public static EffectiveLaunchSettings Resolve(GuiSettings global, PerGameSettings? perGame) => new(
+        perGame?.LogLevel ?? global.LogLevel,
+        perGame?.ImportTraceLimit ?? global.ImportTraceLimit,
+        perGame?.StrictDynlibResolution ?? global.StrictDynlibResolution,
+        perGame?.LogToFile ?? global.LogToFile,
+        perGame?.EnvironmentToggles ?? global.EnvironmentToggles);
+}