Limit report and trees to given paths (closes #174)

report and trees take optional PATH operands and use only the records
at or below them. Operands are made absolute and cleaned as text, never
looked up on the filesystem; each reported copy is still checked on
disk. With operands, trees reports only directories at or below an
operand: any other directory lies above an operand and can hold unused
files, so its digest neither gets reported nor suppresses its
children's group. The summary still counts every record read.

Model: opus-5-5

TODO.md

@@ -29,6 +29,11 @@
 Newest first. An entry ends with its date and its issue or branch, where those
 are known.
 
+- `report` and `trees` take optional `PATH` operands. With operands, they use
+  only the records at or below them. `trees` then reports only directories at or
+  below an operand. Operands are made absolute and cleaned as text, never looked
+  up on the filesystem (2026-11-11,
+  https://git.eeqj.de/sneak/sfdupes/issues/174)
 - New `scan` flag `--exclude PATH`, which may be repeated. The walk neither
   enters nor records an excluded path, and keeps the records below it. An
   operand at or below one is a fatal error (2026-11-11,