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/generate_model_inputs.Rd

@@ -5,9 +5,9 @@
 \title{Generate Resampled Model Inputs}
 \usage{
 generate_model_inputs(
-  feature_prefix = "04_feature/variant=Base",
-  out_prefix = "05_model_input",
-  bucket_name = "baf-fraud"
+  feature_prefix = "baf-fraud/04_feature/variant=Base",
+  out_prefix = "baf-fraud/05_model_input",
+  bucket_name = "lake"
 )
 }
 \arguments{
@@ -15,7 +15,7 @@ generate_model_inputs(
 
 \item{out_prefix}{Character. Output prefix base (e.g., "05_model_input").}
 
-\item{bucket_name}{Character. Bucket name. Default "baf-fraud".}
+\item{bucket_name}{Character. Bucket name. Default "lake".}
 }
 \value{
 Character. The output prefix (for targets dependency tracking).