refactor(abstractions): rename ILogger to IPluginLogger, doc Initialize

Addresses code quality review of ed1c2d0:
- ILogger would collide with Microsoft.Extensions.Logging.ILogger and Serilog.ILogger
  in any plugin file that imports both namespaces; renamed to IPluginLogger
- IAcDreamPlugin.Initialize now has an XML doc clarifying its lifecycle contract

src/AcDream.Plugin.Abstractions/IAcDreamPlugin.cs

@@ -3,7 +3,12 @@ namespace AcDream.Plugin.Abstractions;
 
 public interface IAcDreamPlugin
 {
+    /// <summary>
+    /// Called exactly once, before <see cref="Enable"/>. The plugin should stash the
+    /// host reference and do any one-time setup that doesn't depend on a connected world.
+    /// </summary>
     void Initialize(IPluginHost host);
+
     void Enable();
     void Disable();
 }