feat(di): scaffold Microsoft.Extensions.Hosting container (DI-1 + DI-1b)

Lays down the DI foundation that v1.5.x will run on top of, without
flipping the switch on Plugin.cs yet (that move follows in C3). The new
files compile alongside the existing bootstrap but no caller resolves
the host, so the live behaviour is byte-identical to v1.4.10.

What's new:

- PluginHostFactory.cs: HostBuilder.Build(plugin, dependencies)
  registers ~46 services across Block A (21 Dalamud singletons), Block
  B (14 HellionChat services plus FileDialogManager), Block C (8
  windows), plus Plugin and PluginLifecycle. Service-class bodies are
  untouched - Plugin-backref ctors go through factory lambdas.
- PluginLifecycle.cs: thin IAsyncDisposable wrapping the host's
  StartAsync/StopAsync, with idempotent dispose and framework-thread
  Host.Dispose. The Host is assigned via a property setter from
  Plugin.ctor; HellionChat deviates from Lightless' Func-delegate
  pattern because the schema gate must run before Build.
- Infrastructure/Logging/{DalamudLogger, DalamudLoggingProvider,
  DalamudLoggingProviderExtensions}.cs: ILogger<T> -> IPluginLog
  bridge, ported from Lightless without the mod-sync hasModifiedGameFiles
  flag and without the LightlessConfigService log-level coupling.
- Infrastructure/Hosting/InitHostedServices.cs: seven IHostedService
  adapters around the existing init methods (FontManager.BuildFonts,
  ThemeRegistry warmup+switch, IpcManager/TypingIpc/ExtraChat eager
  resolve, MessageManager.FilterAllTabsAsync, AutoTellTabsService
  .Initialize). Adapter style rather than inlining ": IHostedService"
  on the service classes per the DI-2a "service bodies untouched"
  constraint.

Plan drift noted for cycle closure: MessageStore stays inside
MessageManager.ctor (not a standalone container singleton) because
MessageManager.ctor allocates it directly today; promoting it would
double-construct the SQLite handle. AutoTellTabsService reads it via
MessageManager.Store inside its factory lambda.

HellionChat/Infrastructure/Hosting/InitHostedServices.cs

@@ -0,0 +1,103 @@
+using Dalamud.Plugin;
+using HellionChat.Ipc;
+using HellionChat.Themes;
+using Microsoft.Extensions.Hosting;
+
+namespace HellionChat.Infrastructure.Hosting;
+
+// Adapter shells around the IHostedService contract so the host can resolve
+// the underlying singletons eagerly and trigger their existing init methods
+// without modifying the service class bodies (DI-2a constraint). Bodies that
+// stay empty here still serve a purpose: the host resolves the service when
+// it instantiates the hosted service, which forces the ctor (IPC subscribe
+// for IpcManager / TypingIpc / ExtraChat) to run during StartAsync instead of
+// lazily on first GetRequiredService.
+
+internal sealed class FontManagerInitHostedService(FontManager fontManager) : IHostedService
+{
+    public Task StartAsync(CancellationToken cancellationToken)
+    {
+        fontManager.BuildFonts();
+        return Task.CompletedTask;
+    }
+
+    public Task StopAsync(CancellationToken cancellationToken) => Task.CompletedTask;
+}
+
+internal sealed class ThemeRegistryInitHostedService(ThemeRegistry registry) : IHostedService
+{
+    public Task StartAsync(CancellationToken cancellationToken)
+    {
+        // Materialise the lazy AllCustom enumerable so the slug lookup hits a
+        // warm cache; otherwise the first Switch falls through to the built-in
+        // default when Config.Theme points at a custom slug.
+        foreach (var _ in registry.AllCustom()) { }
+        registry.Switch(Plugin.Config.Theme);
+        return Task.CompletedTask;
+    }
+
+    public Task StopAsync(CancellationToken cancellationToken) => Task.CompletedTask;
+}
+
+// IPC subscribers do their wiring in the ctor today, so StartAsync stays a
+// no-op — the value of registering them as hosted services is that the host
+// resolves them eagerly during Build, which triggers the ctor work. Moving
+// the body into StartAsync is a DI-2b follow-up after the service ctors are
+// allowed to change.
+
+internal sealed class IpcManagerInitHostedService(IpcManager ipc) : IHostedService
+{
+    private readonly IpcManager _ipc = ipc;
+
+    public Task StartAsync(CancellationToken cancellationToken) => Task.CompletedTask;
+
+    public Task StopAsync(CancellationToken cancellationToken) => Task.CompletedTask;
+}
+
+internal sealed class TypingIpcInitHostedService(TypingIpc typingIpc) : IHostedService
+{
+    private readonly TypingIpc _typingIpc = typingIpc;
+
+    public Task StartAsync(CancellationToken cancellationToken) => Task.CompletedTask;
+
+    public Task StopAsync(CancellationToken cancellationToken) => Task.CompletedTask;
+}
+
+internal sealed class ExtraChatInitHostedService(ExtraChat extraChat) : IHostedService
+{
+    private readonly ExtraChat _extraChat = extraChat;
+
+    public Task StartAsync(CancellationToken cancellationToken) => Task.CompletedTask;
+
+    public Task StopAsync(CancellationToken cancellationToken) => Task.CompletedTask;
+}
+
+internal sealed class MessageManagerInitHostedService(
+    IDalamudPluginInterface pluginInterface,
+    MessageManager manager
+) : IHostedService
+{
+    public Task StartAsync(CancellationToken cancellationToken)
+    {
+        // FilterAllTabsAsync rebuilds the per-tab view from the message store;
+        // on Boot, tabs come up empty and the first chat events fill them, so
+        // we skip the rebuild to avoid a pointless full-history scan.
+        if (pluginInterface.Reason is not PluginLoadReason.Boot)
+            manager.FilterAllTabsAsync();
+        return Task.CompletedTask;
+    }
+
+    public Task StopAsync(CancellationToken cancellationToken) => Task.CompletedTask;
+}
+
+internal sealed class AutoTellTabsServiceInitHostedService(AutoTellTabsService service)
+    : IHostedService
+{
+    public Task StartAsync(CancellationToken cancellationToken)
+    {
+        service.Initialize();
+        return Task.CompletedTask;
+    }
+
+    public Task StopAsync(CancellationToken cancellationToken) => Task.CompletedTask;
+}

HellionChat/Infrastructure/Logging/DalamudLogger.cs

@@ -0,0 +1,62 @@
+using System.Text;
+using Dalamud.Plugin.Services;
+using Microsoft.Extensions.Logging;
+
+namespace HellionChat.Infrastructure.Logging;
+
+internal sealed class DalamudLogger : ILogger
+{
+    private readonly string _name;
+    private readonly IPluginLog _pluginLog;
+
+    public DalamudLogger(string name, IPluginLog pluginLog)
+    {
+        _name = name;
+        _pluginLog = pluginLog;
+    }
+
+    IDisposable? ILogger.BeginScope<TState>(TState state) => default!;
+
+    // Filtering happens in Dalamud's /xllog. Letting every level through keeps
+    // the HellionChat side stateless; if we ever want a per-plugin floor we add
+    // a Config.LogLevel and tighten this method.
+    public bool IsEnabled(LogLevel logLevel) => true;
+
+    public void Log<TState>(
+        LogLevel logLevel,
+        EventId eventId,
+        TState state,
+        Exception? exception,
+        Func<TState, Exception?, string> formatter
+    )
+    {
+        if (!IsEnabled(logLevel))
+            return;
+
+        if ((int)logLevel <= (int)LogLevel.Information)
+        {
+            _pluginLog.Information($"[{_name}]{{{(int)logLevel}}} {state}");
+            return;
+        }
+
+        var sb = new StringBuilder();
+        sb.Append($"[{_name}]{{{(int)logLevel}}} {state} {exception?.Message}");
+        if (!string.IsNullOrWhiteSpace(exception?.StackTrace))
+            sb.AppendLine(exception.StackTrace);
+
+        var inner = exception?.InnerException;
+        while (inner != null)
+        {
+            sb.AppendLine($"InnerException {inner}: {inner.Message}");
+            sb.AppendLine(inner.StackTrace);
+            inner = inner.InnerException;
+        }
+
+        if (logLevel == LogLevel.Warning)
+            _pluginLog.Warning(sb.ToString());
+        else if (logLevel == LogLevel.Error)
+            _pluginLog.Error(sb.ToString());
+        else
+            _pluginLog.Fatal(sb.ToString());
+    }
+}

HellionChat/Infrastructure/Logging/DalamudLoggingProvider.cs

@@ -0,0 +1,44 @@
+using System.Collections.Concurrent;
+using Dalamud.Plugin.Services;
+using Microsoft.Extensions.Logging;
+
+namespace HellionChat.Infrastructure.Logging;
+
+[ProviderAlias("Dalamud")]
+public sealed class DalamudLoggingProvider : ILoggerProvider
+{
+    private readonly ConcurrentDictionary<string, DalamudLogger> _loggers = new(
+        StringComparer.OrdinalIgnoreCase
+    );
+
+    private readonly IPluginLog _pluginLog;
+
+    public DalamudLoggingProvider(IPluginLog pluginLog)
+    {
+        _pluginLog = pluginLog;
+    }
+
+    public ILogger CreateLogger(string categoryName)
+    {
+        // Category-name normalisation mirrors Lightless: take the leaf type
+        // name, then either ellipsis-trim long ones or left-pad short ones to
+        // 15 chars so the xllog column stays aligned across services.
+        var catName = categoryName.Split(".", StringSplitOptions.RemoveEmptyEntries).Last();
+        if (catName.Length > 15)
+            catName = string.Concat(
+                catName.AsSpan(0, 6),
+                "...",
+                catName.AsSpan(catName.Length - 6, 6)
+            );
+        else
+            catName = catName.PadLeft(15);
+
+        return _loggers.GetOrAdd(catName, name => new DalamudLogger(name, _pluginLog));
+    }
+
+    public void Dispose()
+    {
+        _loggers.Clear();
+        GC.SuppressFinalize(this);
+    }
+}

HellionChat/Infrastructure/Logging/DalamudLoggingProviderExtensions.cs

@@ -0,0 +1,23 @@
+using Dalamud.Plugin.Services;
+using Microsoft.Extensions.DependencyInjection;
+using Microsoft.Extensions.DependencyInjection.Extensions;
+using Microsoft.Extensions.Logging;
+
+namespace HellionChat.Infrastructure.Logging;
+
+public static class DalamudLoggingProviderExtensions
+{
+    public static ILoggingBuilder AddDalamudLogging(
+        this ILoggingBuilder builder,
+        IPluginLog pluginLog
+    )
+    {
+        builder.ClearProviders();
+        builder.Services.TryAddEnumerable(
+            ServiceDescriptor.Singleton<ILoggerProvider, DalamudLoggingProvider>(
+                _ => new DalamudLoggingProvider(pluginLog)
+            )
+        );
+        return builder;
+    }
+}