feat(logging): add strategy selection logging to GeneralizedKMeans

Add detailed logging when GeneralizedKMeans selects assignment, update, and
empty cluster handling strategies. This helps users understand which strategy
was chosen (especially important for "auto" assignment mode) and aids
troubleshooting performance issues.

Log output example:
```
Strategy selection: assignment=AutoAssignment, update=GradMeanUDAFUpdate,
  emptyHandler=ReseedRandomHandler
```

This addresses ACTION_ITEMS Production Blockers B (assignment scalability)
and I (API clarity & parameter semantics) by making strategy selection
transparent to users.

Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

Author: derrickburns

src/main/scala/com/massivedatascience/clusterer/ml/GeneralizedKMeans.scala

@@ -127,6 +127,11 @@ class GeneralizedKMeans(override val uid: String)
     val convergence  = new MovementConvergence()
     val validator    = new StandardInputValidator()
 
+    logInfo(
+      s"Strategy selection: assignment=${assigner.getClass.getSimpleName}, " +
+        s"update=${updater.getClass.getSimpleName}, emptyHandler=${emptyHandler.getClass.getSimpleName}"
+    )
+
     // Create config
     val config = LloydsConfig(
       k = $(k),