refactor(di): migrate Root + Misc to ILogger<T> (DI-4 Slice D)

Slice D shrinks vs the original plan: three of the six files cannot
take an ILogger ctor arg without breaking external contracts.

Migrated (8 LogProxy sites across 4 files):
- Commands: 2 sites (Warning, Error). New ctor takes ILogger<Commands>.
- Themes/ThemeRegistry: 1 site (Debug). ILogger<ThemeRegistry>? is
  optional (default null) so the existing Build-Suite tests that
  construct `new ThemeRegistry()` parameterless keep working without
  changes. _logger?.LogDebug guards the call site.
- PayloadHandler: 3 sites (Error, Warning, Error). New ctor takes
  ILogger<PayloadHandler>. ChatLogWindow's two `new PayloadHandler(this)`
  sites (the direct field and the Lender lambda) now hand a fresh
  CreateLogger<PayloadHandler>() from the existing _loggerFactory.

Not migrated (5 sites stay on Plugin.LogProxy, plan drifts D12-D14):
- D12 - Configuration (1 site): IPluginConfiguration, instantiated by
  Dalamud's Interface.GetPluginConfig() via reflection on the
  parameterless ctor. Adding an ILogger arg would break GetPluginConfig.
- D13 - Message (4 sites): partial data class with two ctor overloads,
  mass-instantiated across 3 plugin sites plus Newtonsoft JSON
  deserialisation. Ctor extension would be invasive across ~20 call
  sites with low payoff (data-class logger is unusual).
- D14 - FontManager (2 sites): both Plugin.LogProxy calls live in
  static methods (TryGetHellionFontBytes, AddFontWithFallback) that
  cannot reach an instance _logger. Same root cause as D8 in
  GameFunctions. FontManager joins the static-bucket alongside
  EmoteCache et al.; the ctor + _logger field added mid-Slice-D were
  rolled back to keep the class clean.

Plugin.LogProxy surface after C9 (8 file buckets, ~12 sites total):
- 4 originally-static consumers: EmoteCache, AutoTranslate,
  MemoryUtil, WrapperUtil
- 3 cannot-take-ctor-arg consumers: Configuration, Message, FontManager
- 1 single-static-method consumer: GameFunctions.TryOpenAdventurerPlate
  (D8 from Slice B)

Smoke 2 is now due.

HellionChat/Commands.cs

@@ -1,10 +1,17 @@
 using Dalamud.Game.Command;
+using Microsoft.Extensions.Logging;
 
 namespace HellionChat;
 
 internal sealed class Commands : IDisposable
 {
     private readonly Dictionary<string, CommandWrapper> Registered = [];
+    private readonly ILogger<Commands> _logger;
+
+    public Commands(ILogger<Commands> logger)
+    {
+        _logger = logger;
+    }
 
     public void Dispose()
     {
@@ -52,7 +59,7 @@ internal sealed class Commands : IDisposable
     {
         if (!Registered.TryGetValue(command, out var wrapper))
         {
-            Plugin.LogProxy.Warning($"Missing registration for command {command}");
+            _logger.LogWarning($"Missing registration for command {command}");
             return;
         }
 
@@ -62,7 +69,7 @@ internal sealed class Commands : IDisposable
         }
         catch (Exception ex)
         {
-            Plugin.LogProxy.Error(ex, $"Error while executing command {command}");
+            _logger.LogError(ex, $"Error while executing command {command}");
         }
     }
 }