feat(util): add IPluginLogProxy interface and production wrapper

F12.2 closes the gap that F12.1 left open: MessageStore's ctor calls
Plugin.Log.Information inside Migrate0, which prevents an isolated xUnit
construction test (Dalamud.dll cannot load in the test AppDomain).

The proxy mirrors IPluginLog's full surface (Verbose/Debug/Information/
Info/Warning/Error/Fatal — both Info and Information as Dalamud exposes
them) with both single-string and Exception+string overloads, so the
~91 existing Plugin.Log.* call-sites become a drop-in rewrite to
Plugin.LogProxy.*.

A later DI-container adoption cycle (v1.5.x) may swap this for
Microsoft.Extensions.Logging's ILogger<T>; this commit is the
intermediate decorator step.

HellionChat/Plugin.cs

@@ -117,6 +117,11 @@ public sealed class Plugin : IAsyncDalamudPlugin
     // any service allocated in LoadAsync can read Plugin.PlatformUtil.
     internal static IPlatformUtil PlatformUtil { get; private set; } = null!;
 
+    // Log indirection over Dalamud's IPluginLog. Same rationale as PlatformUtil:
+    // call-sites read through LogProxy so MessageStore can be tested in
+    // isolation. Wired immediately after Dalamud injects Log.
+    internal static IPluginLogProxy LogProxy { get; private set; } = null!;
+
     // Idempotency guard — Dalamud may fire DisposeAsync twice in a reload race.
     private int _disposeStarted;
 
@@ -162,6 +167,7 @@ public sealed class Plugin : IAsyncDalamudPlugin
         // needs Util.* — services then read Plugin.PlatformUtil instead of
         // hitting the Dalamud static surface directly.
         PlatformUtil = new DalamudPlatformUtil();
+        LogProxy = new DalamudPluginLogProxy(Log);
 
         // Schema gate: v1.4.x requires config v16. Users on older schemas
         // must install v1.4.2 first to run the migration chain.

HellionChat/Util/DalamudPluginLogProxy.cs

@@ -0,0 +1,40 @@
+using System;
+using Dalamud.Plugin.Services;
+
+namespace HellionChat.Util;
+
+internal sealed class DalamudPluginLogProxy : IPluginLogProxy
+{
+    private readonly IPluginLog _log;
+
+    public DalamudPluginLogProxy(IPluginLog log) => _log = log;
+
+    public void Verbose(string message) => _log.Verbose(message);
+
+    public void Verbose(Exception exception, string message) => _log.Verbose(exception, message);
+
+    public void Debug(string message) => _log.Debug(message);
+
+    public void Debug(Exception exception, string message) => _log.Debug(exception, message);
+
+    public void Information(string message) => _log.Information(message);
+
+    public void Information(Exception exception, string message) =>
+        _log.Information(exception, message);
+
+    public void Info(string message) => _log.Info(message);
+
+    public void Info(Exception exception, string message) => _log.Info(exception, message);
+
+    public void Warning(string message) => _log.Warning(message);
+
+    public void Warning(Exception exception, string message) => _log.Warning(exception, message);
+
+    public void Error(string message) => _log.Error(message);
+
+    public void Error(Exception exception, string message) => _log.Error(exception, message);
+
+    public void Fatal(string message) => _log.Fatal(message);
+
+    public void Fatal(Exception exception, string message) => _log.Fatal(exception, message);
+}

HellionChat/Util/IPluginLogProxy.cs

@@ -0,0 +1,33 @@
+using System;
+
+namespace HellionChat.Util;
+
+// Indirection over Dalamud's IPluginLog so MessageStore can be constructed
+// in an isolated xUnit AppDomain without loading Dalamud.dll — same pattern
+// as IPlatformUtil from F12.1. A later DI-container cycle (v1.5.x) may
+// replace this with Microsoft.Extensions.Logging's ILogger<T>.
+internal interface IPluginLogProxy
+{
+    void Verbose(string message);
+    void Verbose(Exception exception, string message);
+
+    void Debug(string message);
+    void Debug(Exception exception, string message);
+
+    void Information(string message);
+    void Information(Exception exception, string message);
+
+    // IPluginLog exposes Info as a distinct method (short alias of
+    // Information) — both are present so call-sites stay drop-in.
+    void Info(string message);
+    void Info(Exception exception, string message);
+
+    void Warning(string message);
+    void Warning(Exception exception, string message);
+
+    void Error(string message);
+    void Error(Exception exception, string message);
+
+    void Fatal(string message);
+    void Fatal(Exception exception, string message);
+}