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/clean_baf_base.Rd

@@ -6,8 +6,8 @@
 \usage{
 clean_baf_base(
   in_prefix,
-  out_prefix = "03_primary/variant=Base",
-  bucket_name = "baf-fraud",
+  out_prefix = "baf-fraud/03_primary/variant=Base",
+  bucket_name = "lake",
   partitioning = "month",
   existing_data_behavior = c("overwrite", "error", "delete_matching"),
   verbose = TRUE
@@ -18,7 +18,7 @@ clean_baf_base(
 
 \item{out_prefix}{Character. Output dataset prefix inside bucket (e.g. "03_primary/variant=Base").}
 
-\item{bucket_name}{Character. Bucket name. Default "baf-fraud".}
+\item{bucket_name}{Character. Bucket name. Default "lake".}
 
 \item{partitioning}{Character vector of columns to partition by. Default "month". Set NULL to disable.}