Reorganize docs into category folders and drop the retired head-review page

Group the top-level docs into docs/project, docs/design, docs/assets and
docs/process, each with its own README index. Delete the superseded
docs/screens/head-review page and sheets. Rewrite every markdown link,
absolute docs path and tool/test reference to the new locations, fix the
pre-existing broken anchors and remove the dead Joke Shop photo-board link.
check_docs OK, Python tooling 167/167.

docs/screens/refs/README.md

@@ -76,8 +76,8 @@ committed here is the redacted copy, not the original.
 ## How the folder is used
 
 - Build the venue **three-up boards** (photo | concept | current capture) for the review verdicts.
-- Link the board from the venue map document (`docs/venues.md#hollywood-boulevard`,
-  `docs/venues.md#the-joke-shop`) and from the local-map block notes.
+- Link the board from the venue map document (`docs/design/venues.md#hollywood-boulevard`,
+  `docs/design/venues.md#the-joke-shop`) and from the local-map block notes.
 - Cite the sidecar when a texture, proportion or signage decision is derived from a photo.
 - Refresh the board when a venue change makes an old reference misleading, and note the change in
   the sidecar.