Removing an empty file frees nothing, yet every `.gitkeep`,
`__init__.py` and empty log formed one `report` group, and directories
holding only empty files were reported as 0-byte duplicate trees. Now
`report` writes no group of size 0 and `trees` writes no group whose
trees hold 0 bytes. An empty file still counts toward the digest of a
tree that holds other files. No option, as approved on the issue. The
README's definition-of-done test now expects `empty1` and `empty2`
nowhere.
Model: opus-5-5
clawbot