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 Delete the superseded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/process/README.md

@@ -0,0 +1,11 @@
+# Process Documentation
+
+Setup, quality assurance and releasing.
+
+- [`getting-started.md`](getting-started.md) — setup, run/test commands, controls and save data.
+- [`release-qa.md`](release-qa.md) — the manual smoke checklist and the balance-acceptance
+  protocol.
+- [`RELEASING.md`](RELEASING.md) — export templates, release build, CI/publishing and rollback.
+
+Up: [`../README.md`](../README.md) · Product plan: [`../../PLAN.md`](../../PLAN.md) · Tasks:
+[`../../TODO.md`](../../TODO.md).