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/IPluginHost.cs

@@ -3,9 +3,9 @@ namespace AcDream.Plugin.Abstractions;
 
 /// <summary>
 /// Entry point for a plugin into the acdream runtime. The surface will grow
-/// across phases as more systems come online. For Phase 1 only ILogger is real.
+/// across phases as more systems come online. For Phase 1 only IPluginLogger is real.
 /// </summary>
 public interface IPluginHost
 {
-    ILogger Log { get; }
+    IPluginLogger Log { get; }
 }