Address review: remove stray files, use proportional blob sizing

- Remove .claude/ and stray .md files from previous work
- Change blob size approximation from linked_ssts approach to
  proportional: blob_size_in_range = total_blob_size *
  (sst_size_in_range / total_sst_size)
- Update test to verify proportional behavior (partial range
  returns less than full range)
- Update API comment to describe the proportional approach

Author: xingbowang