Resolve scan operands to their real paths (closes #144)

scan now resolves every operand with its symlinks followed before the
walk, and uses that real path for pruning, walking, records and
warnings. A relative operand is joined to the working directory as the
kernel reports it, so a ".." after a symlink counts from its target, as
with realpath. A symlink operand is scanned at its target instead of
skipped. An operand given through a symlink below another operand, to a
directory outside it, is walked on its own instead of dropped with its
records deleted. An operand that cannot be resolved is a fatal error
naming the operand as given. The walk itself still follows no symlink.

Model: opus-5-5

TODO.md

@@ -29,6 +29,12 @@
 Newest first. An entry ends with its date and its issue or branch, where those
 are known.
 
+- `scan` resolves each operand to its real path, symlinks followed, before the
+  walk. A symlink operand is scanned at its target instead of skipped. With
+  `/srv/link` a symlink to a directory outside `/srv`, `scan /srv /srv/link/sub`
+  walks `sub` on its own instead of dropping it and deleting its records
+  (2026-11-06, https://git.eeqj.de/sneak/sfdupes/issues/144)
+
 - `README.md` and a comment in `scan.go` no longer say ZFS counts a new file's
   blocks only seconds after the write. The count can land in under a second.
   Both now say up to seconds after the write, as the comment on `diskSizeOf` in