feat: watch the profiles that declare no files

An empty file list is the one assertion here that ages unwatched. Nothing
can go missing and no ref can drift, so nothing notices when a core that
embedded everything grows a path. virtualjaguar said "No external BIOS
files are required or loaded by this core" while its source had grown
eleven filenames read from the system directory, and only a reading
found it.

fileless_audit looks for the request itself, the system directory ask, in
the sources each profile already cites. Over the 151 fileless profiles it
named eleven, of which two were covered by data_directories, six carried
an exclusion_note, and three had nothing written down at all: craft
writes its world database in that directory, dice stores the answer in a
variable no other file in the tree names, lutro hands it to the Lua game.
Each now says so.

The check settles: declared files, a declared directory, or a written
answer all end it, so what it reports is the set nobody has read yet. A
test holds the corpus at zero.

wiki/tools.md

@@ -238,6 +238,33 @@ to the files inside the archive, so the exported DAT lists those entries
 without a container sha1. Anyone submitting the DAT upstream should mention
 this.
 
+### fileless_audit.py
+
+Names the profiles that declare no files whose source asks for a directory to
+read from.
+
+```bash
+python scripts/fileless_audit.py craft dice lutro
+```
+
+An empty `files:` list is the one assertion in the repository that ages
+unwatched: there is no file to go missing and no ref to drift, so nothing
+notices when a core that embedded everything grows a path. virtualjaguar
+carried "No external BIOS files are required or loaded by this core" while its
+source had grown eleven filenames read from the system directory.
+
+The signal is the request itself, `RETRO_ENVIRONMENT_GET_SYSTEM_DIRECTORY` and
+its spellings, looked for in the sources the profile already cites. Finding one
+does not prove a file is loaded, which is why this reports rather than
+concludes.
+
+Three answers settle a profile and it is not reported again: it declares files,
+it declares `data_directories` (dinothawr reads `system_dir/dinothawr/` and
+says so there), or it carries an `exclusion_note` saying what the directory is
+for. craft writes its world database in it, dice stores the answer in a
+variable no other file names, lutro hands it to the Lua game. What is left is
+the set nobody has read yet, which is the only set worth reading.
+
 ### mame_ref_audit.py
 
 Checks that each MAME romset ref names the line declaring its own set, at the