dwim: take the scan flags (closes #162)

dwim now takes --workers, -x, --no-default-excludes and --exclude with
the meaning they have for scan. One scanOptions struct, one function
that adds the flags and one PreRunE check serve both commands, and
runScan takes the struct instead of four separate values. The dwim help
says that the scan runs with the same flags, and lists the default
excludes, as the scan help does.

Model: opus-5-5

TODO.md

@@ -29,6 +29,10 @@
 Newest first. An entry ends with its date and its issue or branch, where those
 are known.
 
+- `dwim` takes the `scan` flags `--workers`, `-x`, `--no-default-excludes` and
+  `--exclude`, with the same meaning. Both commands register and check them with
+  the same code (2026-11-11, https://git.eeqj.de/sneak/sfdupes/issues/162)
+
 - The help of `sfdupes` and of `scan` names the database, its default path and
   `SFDUPES_DATABASE`. The help of `report` and `trees` lists the columns, the
   order of the rows and the escapes. The help of `info` lists its lines. The