Refactor bucket structure: baf-fraud/ prefix under lake bucket

All functions now default to bucket_name = "lake" with "baf-fraud/"
prepended to all layer prefixes, matching the contemporary lakehouse
naming convention (one bucket per environment, project as prefix).

Migration: copy baf-fraud/ data to lake/baf-fraud/ on analyticsvm,
update BAF_BUCKET env var from "baf-fraud" to "lake".

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

man/run_imbalance_tournament.Rd

@@ -8,8 +8,8 @@ run_imbalance_tournament(
   tasks,
   windows,
   feature_prefix,
-  bucket_name = "baf-fraud",
-  inputs_prefix = "05_model_input"
+  bucket_name = "lake",
+  inputs_prefix = "baf-fraud/05_model_input"
 )
 }
 \arguments{
@@ -19,7 +19,7 @@ run_imbalance_tournament(
 
 \item{feature_prefix}{Character. The upstream dependency prefix (used to force DAG execution).}
 
-\item{bucket_name}{Character. Bucket name. Default "baf-fraud".}
+\item{bucket_name}{Character. Bucket name. Default "lake".}
 
 \item{inputs_prefix}{Character. The folder containing the sampled data. Default "05_model_input".}
 }